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 $87.38   11.719%   $97.6201   $97.62   $97.60   $97.60  
  Purchase #2 $72.88   10.549%   $80.5681   $80.57   $80.55   $80.60  
  Purchase #3 $104.52   5.566%   $110.3376   $110.34   $110.35   $110.30  
  Purchase #4 $158.52   11.666%   $177.0129   $177.01   $177.00   $177.00  
  Purchase #5 $152.63   3.391%   $157.8057   $157.81   $157.80   $157.80  
  Purchase #6 $98.81   13.310%   $111.9616   $111.96   $111.95   $112.00  
  Purchase #7 $244.32   9.129%   $266.624   $266.62   $266.60   $266.60  
  7 purchase totals = $919.06       $1,001.9300   $1,001.93   $1,001.85   $1,001.90