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 $83.46   11.852%   $93.3517   $93.35   $93.35   $93.40  
  Purchase #2 $199.86   13.383%   $226.6073   $226.61   $226.60   $226.60  
  Purchase #3 $250.57   11.719%   $279.9343   $279.93   $279.95   $279.90  
  Purchase #4 $172.31   5.591%   $181.9439   $181.94   $181.95   $181.90  
  Purchase #5 $184.94   3.119%   $190.7083   $190.71   $190.70   $190.70  
  Purchase #6 $195.31   10.826%   $216.4543   $216.45   $216.45   $216.50  
  Purchase #7 $12.55   3.255%   $12.9585   $12.96   $12.95   $13.00  
  7 purchase totals = $1,099.00       $1,201.9583   $1,201.95   $1,201.95   $1,202.00