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 $228.42   6.800%   $243.9526   $243.95   $243.95   $244.00  
  Purchase #2 $194.58   8.846%   $211.7925   $211.79   $211.80   $211.80  
  Purchase #3 $185.52   11.283%   $206.4522   $206.45   $206.45   $206.50  
  Purchase #4 $119.26   11.454%   $132.92   $132.92   $132.90   $132.90  
  Purchase #5 $82.94   10.457%   $91.613   $91.61   $91.60   $91.60  
  Purchase #6 $161.38   9.473%   $176.6675   $176.67   $176.65   $176.70  
  Purchase #7 $72.67   9.761%   $79.7633   $79.76   $79.75   $79.80  
  7 purchase totals = $1,044.77       $1,143.1611   $1,143.15   $1,143.10   $1,143.30