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 $87.59   11.767%   $97.8967   $97.90   $97.90   $97.90  
  Purchase #2 $54.78   9.850%   $60.1758   $60.18   $60.20   $60.20  
  Purchase #3 $104.47   5.252%   $109.9568   $109.96   $109.95   $110.00  
  Purchase #4 $180.76   4.254%   $188.4495   $188.45   $188.45   $188.40  
  Purchase #5 $218.70   7.711%   $235.564   $235.56   $235.55   $235.60  
  Purchase #6 $163.92   5.439%   $172.8356   $172.84   $172.85   $172.80  
  Purchase #7 $99.63   11.286%   $110.8742   $110.87   $110.85   $110.90  
  7 purchase totals = $909.85       $975.7526   $975.76   $975.75   $975.80