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 $150.50   7.772%   $162.1969   $162.20   $162.20   $162.20  
  Purchase #2 $249.96   11.758%   $279.3503   $279.35   $279.35   $279.40  
  Purchase #3 $12.68   13.448%   $14.3852   $14.39   $14.40   $14.40  
  Purchase #4 $122.61   12.481%   $137.913   $137.91   $137.90   $137.90  
  Purchase #5 $201.33   6.616%   $214.65   $214.65   $214.65   $214.70  
  Purchase #6 $167.95   4.469%   $175.4557   $175.46   $175.45   $175.50  
  Purchase #7 $154.53   4.181%   $160.9909   $160.99   $161.00   $161.00  
  7 purchase totals = $1,059.56       $1,144.9420   $1,144.95   $1,144.95   $1,145.10