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 $233.68   8.773%   $254.1807   $254.18   $254.20   $254.20  
  Purchase #2 $190.85   6.236%   $202.7514   $202.75   $202.75   $202.80  
  Purchase #3 $112.48   10.155%   $123.9023   $123.90   $123.90   $123.90  
  Purchase #4 $126.61   4.222%   $131.9555   $131.96   $131.95   $132.00  
  Purchase #5 $207.53   3.291%   $214.3598   $214.36   $214.35   $214.40  
  Purchase #6 $101.80   13.168%   $115.205   $115.21   $115.20   $115.20  
  Purchase #7 $179.60   5.765%   $189.9539   $189.95   $189.95   $190.00  
  7 purchase totals = $1,152.55       $1,232.3086   $1,232.31   $1,232.30   $1,232.50