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 $68.79   11.612%   $76.7779   $76.78   $76.80   $76.80  
  Purchase #2 $142.92   6.475%   $152.1741   $152.17   $152.15   $152.20  
  Purchase #3 $166.26   5.429%   $175.2863   $175.29   $175.30   $175.30  
  Purchase #4 $25.46   10.476%   $28.1272   $28.13   $28.15   $28.10  
  Purchase #5 $211.90   11.219%   $235.6731   $235.67   $235.65   $235.70  
  Purchase #6 $241.38   6.306%   $256.6014   $256.60   $256.60   $256.60  
  Purchase #7 $230.58   8.569%   $250.3384   $250.34   $250.35   $250.30  
  7 purchase totals = $1,087.29       $1,174.9784   $1,174.98   $1,175.00   $1,175.00