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 $231.52   10.865%   $256.6746   $256.67   $256.65   $256.70  
  Purchase #2 $189.82   13.132%   $214.7472   $214.75   $214.75   $214.70  
  Purchase #3 $98.51   6.354%   $104.7693   $104.77   $104.75   $104.80  
  Purchase #4 $185.33   4.705%   $194.0498   $194.05   $194.05   $194.00  
  Purchase #5 $217.64   11.855%   $243.4412   $243.44   $243.45   $243.40  
  Purchase #6 $152.59   10.696%   $168.911   $168.91   $168.90   $168.90  
  Purchase #7 $135.59   6.109%   $143.8732   $143.87   $143.85   $143.90  
  7 purchase totals = $1,211.00       $1,326.4663   $1,326.46   $1,326.40   $1,326.40