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 $152.58   7.858%   $164.5697   $164.57   $164.55   $164.60  
  Purchase #2 $55.49   12.838%   $62.6138   $62.61   $62.60   $62.60  
  Purchase #3 $231.66   11.311%   $257.8631   $257.86   $257.85   $257.90  
  Purchase #4 $167.53   3.248%   $172.9714   $172.97   $172.95   $173.00  
  Purchase #5 $38.64   10.609%   $42.7393   $42.74   $42.75   $42.70  
  Purchase #6 $225.71   4.717%   $236.3567   $236.36   $236.35   $236.40  
  Purchase #7 $5.63   4.692%   $5.8942   $5.89   $5.90   $5.90  
  7 purchase totals = $877.24       $943.0082   $943.00   $942.95   $943.10