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 $224.65   9.479%   $245.9446   $245.94   $245.95   $245.90  
  Purchase #2 $239.79   7.723%   $258.309   $258.31   $258.30   $258.30  
  Purchase #3 $107.32   7.849%   $115.7435   $115.74   $115.75   $115.70  
  Purchase #4 $244.30   10.383%   $269.6657   $269.67   $269.65   $269.70  
  Purchase #5 $31.90   12.785%   $35.9784   $35.98   $36.00   $36.00  
  Purchase #6 $70.73   4.772%   $74.1052   $74.11   $74.10   $74.10  
  Purchase #7 $49.90   5.386%   $52.5876   $52.59   $52.60   $52.60  
  7 purchase totals = $968.59       $1,052.3340   $1,052.34   $1,052.35   $1,052.30