Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.82   11.714%   $150.6128   $150.61   $150.60   $150.60  
  Purchase #2 $146.95   10.242%   $162.0006   $162.00   $162.00   $162.00  
  Purchase #3 $204.38   9.795%   $224.399   $224.40   $224.40   $224.40  
  Purchase #4 $217.63   6.821%   $232.4745   $232.47   $232.45   $232.50  
  Purchase #5 $224.37   6.165%   $238.2024   $238.20   $238.20   $238.20  
  Purchase #6 $243.56   10.587%   $269.3457   $269.35   $269.35   $269.30  
  Purchase #7 $217.78   13.873%   $247.9926   $247.99   $248.00   $248.00  
  7 purchase totals = $1,389.49       $1,525.0276   $1,525.02   $1,525.00   $1,525.00