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 $32.87   5.627%   $34.7196   $34.72   $34.70   $34.70  
  Purchase #2 $212.85   3.234%   $219.7336   $219.73   $219.75   $219.70  
  Purchase #3 $228.94   11.816%   $255.9916   $255.99   $256.00   $256.00  
  Purchase #4 $175.92   10.443%   $194.2913   $194.29   $194.30   $194.30  
  Purchase #5 $151.88   11.408%   $169.2065   $169.21   $169.20   $169.20  
  Purchase #6 $150.85   5.513%   $159.1664   $159.17   $159.15   $159.20  
  Purchase #7 $195.93   12.357%   $220.1411   $220.14   $220.15   $220.10  
  7 purchase totals = $1,149.24       $1,253.2501   $1,253.25   $1,253.25   $1,253.20