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 $93.54   4.326%   $97.5865   $97.59   $97.60   $97.60  
  Purchase #2 $49.85   8.170%   $53.9227   $53.92   $53.90   $53.90  
  Purchase #3 $8.82   11.555%   $9.8392   $9.84   $9.85   $9.80  
  Purchase #4 $236.51   10.190%   $260.6104   $260.61   $260.60   $260.60  
  Purchase #5 $203.94   5.323%   $214.7957   $214.80   $214.80   $214.80  
  Purchase #6 $195.25   4.463%   $203.964   $203.96   $203.95   $204.00  
  Purchase #7 $207.79   13.340%   $235.5092   $235.51   $235.50   $235.50  
  7 purchase totals = $995.70       $1,076.2277   $1,076.23   $1,076.20   $1,076.20