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 $204.75   8.333%   $221.8118   $221.81   $221.80   $221.80  
  Purchase #2 $188.61   6.731%   $201.3053   $201.31   $201.30   $201.30  
  Purchase #3 $69.39   7.781%   $74.7892   $74.79   $74.80   $74.80  
  Purchase #4 $6.88   6.545%   $7.3303   $7.33   $7.35   $7.30  
  Purchase #5 $185.30   6.612%   $197.552   $197.55   $197.55   $197.60  
  Purchase #6 $49.35   8.480%   $53.5349   $53.53   $53.55   $53.50  
  Purchase #7 $68.70   5.714%   $72.6255   $72.63   $72.65   $72.60  
  7 purchase totals = $772.98       $828.9490   $828.95   $829.00   $828.90