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 $55.53   11.598%   $61.9704   $61.97   $61.95   $62.00  
  Purchase #2 $247.40   5.395%   $260.7472   $260.75   $260.75   $260.70  
  Purchase #3 $163.45   8.826%   $177.8761   $177.88   $177.90   $177.90  
  Purchase #4 $181.38   10.525%   $200.4702   $200.47   $200.45   $200.50  
  Purchase #5 $162.89   4.424%   $170.0963   $170.10   $170.10   $170.10  
  Purchase #6 $174.42   5.259%   $183.5927   $183.59   $183.60   $183.60  
  Purchase #7 $228.48   4.432%   $238.6062   $238.61   $238.60   $238.60  
  7 purchase totals = $1,213.55       $1,293.3591   $1,293.37   $1,293.35   $1,293.40