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 $97.69   10.275%   $107.7276   $107.73   $107.75   $107.70  
  Purchase #2 $63.95   6.293%   $67.9744   $67.97   $67.95   $68.00  
  Purchase #3 $66.60   9.205%   $72.7305   $72.73   $72.75   $72.70  
  Purchase #4 $149.71   12.534%   $168.4747   $168.47   $168.45   $168.50  
  Purchase #5 $184.79   7.626%   $198.8821   $198.88   $198.90   $198.90  
  Purchase #6 $235.92   8.826%   $256.7423   $256.74   $256.75   $256.70  
  Purchase #7 $203.61   3.118%   $209.9586   $209.96   $209.95   $210.00  
  7 purchase totals = $1,002.27       $1,082.4902   $1,082.48   $1,082.50   $1,082.50