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 $88.67   10.223%   $97.7347   $97.73   $97.75   $97.70  
  Purchase #2 $174.27   11.588%   $194.4644   $194.46   $194.45   $194.50  
  Purchase #3 $204.57   10.712%   $226.4835   $226.48   $226.50   $226.50  
  Purchase #4 $140.43   6.449%   $149.4863   $149.49   $149.50   $149.50  
  Purchase #5 $75.48   13.855%   $85.9378   $85.94   $85.95   $85.90  
  Purchase #6 $203.48   8.843%   $221.4737   $221.47   $221.45   $221.50  
  Purchase #7 $41.96   11.668%   $46.8559   $46.86   $46.85   $46.90  
  7 purchase totals = $928.86       $1,022.4363   $1,022.43   $1,022.45   $1,022.50