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 $75.27   9.432%   $82.3695   $82.37   $82.35   $82.40  
  Purchase #2 $100.47   3.177%   $103.6619   $103.66   $103.65   $103.70  
  Purchase #3 $183.27   12.393%   $205.9827   $205.98   $206.00   $206.00  
  Purchase #4 $88.76   10.292%   $97.8952   $97.90   $97.90   $97.90  
  Purchase #5 $146.97   5.815%   $155.5163   $155.52   $155.50   $155.50  
  Purchase #6 $85.56   7.129%   $91.6596   $91.66   $91.65   $91.70  
  Purchase #7 $216.30   11.767%   $241.752   $241.75   $241.75   $241.80  
  7 purchase totals = $896.60       $978.8372   $978.84   $978.80   $979.00