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 $186.93   8.331%   $202.5031   $202.50   $202.50   $202.50  
  Purchase #2 $188.48   12.401%   $211.8534   $211.85   $211.85   $211.90  
  Purchase #3 $228.67   11.176%   $254.2262   $254.23   $254.25   $254.20  
  Purchase #4 $248.85   12.470%   $279.8816   $279.88   $279.90   $279.90  
  Purchase #5 $227.52   5.378%   $239.756   $239.76   $239.75   $239.80  
  Purchase #6 $149.76   11.177%   $166.4987   $166.50   $166.50   $166.50  
  Purchase #7 $8.42   4.300%   $8.7821   $8.78   $8.80   $8.80  
  7 purchase totals = $1,238.63       $1,363.5011   $1,363.50   $1,363.55   $1,363.60