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 $88.62   5.412%   $93.4161   $93.42   $93.40   $93.40  
  Purchase #2 $40.89   3.826%   $42.4545   $42.45   $42.45   $42.50  
  Purchase #3 $64.55   7.431%   $69.3467   $69.35   $69.35   $69.30  
  Purchase #4 $146.83   13.193%   $166.2013   $166.20   $166.20   $166.20  
  Purchase #5 $132.29   8.373%   $143.3666   $143.37   $143.35   $143.40  
  Purchase #6 $147.52   4.402%   $154.0138   $154.01   $154.00   $154.00  
  Purchase #7 $146.93   4.669%   $153.7902   $153.79   $153.80   $153.80  
  7 purchase totals = $767.63       $822.5892   $822.59   $822.55   $822.60