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 $91.49   6.102%   $97.0727   $97.07   $97.05   $97.10  
  Purchase #2 $62.79   6.633%   $66.9549   $66.95   $66.95   $67.00  
  Purchase #3 $112.89   12.265%   $126.736   $126.74   $126.75   $126.70  
  Purchase #4 $209.95   7.573%   $225.8495   $225.85   $225.85   $225.80  
  Purchase #5 $53.31   6.717%   $56.8908   $56.89   $56.90   $56.90  
  Purchase #6 $240.49   11.715%   $268.6634   $268.66   $268.65   $268.70  
  Purchase #7 $9.53   3.665%   $9.8793   $9.88   $9.90   $9.90  
  7 purchase totals = $780.45       $852.0466   $852.04   $852.05   $852.10