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 $47.63   4.520%   $49.7829   $49.78   $49.80   $49.80  
  Purchase #2 $222.63   8.301%   $241.1105   $241.11   $241.10   $241.10  
  Purchase #3 $145.99   8.754%   $158.77   $158.77   $158.75   $158.80  
  Purchase #4 $247.26   8.839%   $269.1153   $269.12   $269.10   $269.10  
  Purchase #5 $51.65   13.600%   $58.6744   $58.67   $58.65   $58.70  
  Purchase #6 $188.93   5.772%   $199.835   $199.84   $199.85   $199.80  
  Purchase #7 $54.85   4.145%   $57.1235   $57.12   $57.10   $57.10  
  7 purchase totals = $958.94       $1,034.4116   $1,034.41   $1,034.35   $1,034.40