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 $180.63   8.387%   $195.7794   $195.78   $195.80   $195.80  
  Purchase #2 $69.89   10.248%   $77.0523   $77.05   $77.05   $77.10  
  Purchase #3 $113.66   4.529%   $118.8077   $118.81   $118.80   $118.80  
  Purchase #4 $71.75   5.557%   $75.7371   $75.74   $75.75   $75.70  
  Purchase #5 $122.89   10.113%   $135.3179   $135.32   $135.30   $135.30  
  Purchase #6 $58.43   10.811%   $64.7469   $64.75   $64.75   $64.70  
  Purchase #7 $243.85   8.493%   $264.5602   $264.56   $264.55   $264.60  
  7 purchase totals = $861.10       $932.0015   $932.01   $932.00   $932.00