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 $38.61   7.505%   $41.5077   $41.51   $41.50   $41.50  
  Purchase #2 $228.57   8.653%   $248.3482   $248.35   $248.35   $248.30  
  Purchase #3 $95.61   13.380%   $108.4026   $108.40   $108.40   $108.40  
  Purchase #4 $194.66   7.582%   $209.4191   $209.42   $209.40   $209.40  
  Purchase #5 $162.88   12.221%   $182.7856   $182.79   $182.80   $182.80  
  Purchase #6 $161.80   11.556%   $180.4976   $180.50   $180.50   $180.50  
  Purchase #7 $88.59   4.467%   $92.5473   $92.55   $92.55   $92.50  
  7 purchase totals = $970.72       $1,063.5081   $1,063.52   $1,063.50   $1,063.40