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 $222.86   8.399%   $241.578   $241.58   $241.60   $241.60  
  Purchase #2 $69.39   8.494%   $75.284   $75.28   $75.30   $75.30  
  Purchase #3 $249.66   13.210%   $282.6401   $282.64   $282.65   $282.60  
  Purchase #4 $226.36   12.633%   $254.9561   $254.96   $254.95   $255.00  
  Purchase #5 $100.35   5.402%   $105.7709   $105.77   $105.75   $105.80  
  Purchase #6 $234.63   5.315%   $247.1006   $247.10   $247.10   $247.10  
  Purchase #7 $199.77   8.171%   $216.0932   $216.09   $216.10   $216.10  
  7 purchase totals = $1,303.02       $1,423.4229   $1,423.42   $1,423.45   $1,423.50