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 $183.42   11.637%   $204.7646   $204.76   $204.75   $204.80  
  Purchase #2 $142.75   13.209%   $161.6058   $161.61   $161.60   $161.60  
  Purchase #3 $172.61   4.291%   $180.0167   $180.02   $180.00   $180.00  
  Purchase #4 $244.82   4.456%   $255.7292   $255.73   $255.75   $255.70  
  Purchase #5 $116.42   13.241%   $131.8352   $131.84   $131.85   $131.80  
  Purchase #6 $240.51   10.604%   $266.0137   $266.01   $266.00   $266.00  
  Purchase #7 $50.39   5.178%   $52.9992   $53.00   $53.00   $53.00  
  7 purchase totals = $1,150.92       $1,252.9644   $1,252.97   $1,252.95   $1,252.90