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 $35.49   7.365%   $38.1038   $38.10   $38.10   $38.10  
  Purchase #2 $220.72   9.497%   $241.6818   $241.68   $241.70   $241.70  
  Purchase #3 $159.30   11.624%   $177.817   $177.82   $177.80   $177.80  
  Purchase #4 $58.73   9.706%   $64.4303   $64.43   $64.45   $64.40  
  Purchase #5 $99.33   5.544%   $104.8369   $104.84   $104.85   $104.80  
  Purchase #6 $186.76   10.623%   $206.5995   $206.60   $206.60   $206.60  
  Purchase #7 $116.86   4.438%   $122.0462   $122.05   $122.05   $122.00  
  7 purchase totals = $877.19       $955.5155   $955.52   $955.55   $955.40