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 $35.84   6.804%   $38.2786   $38.28   $38.30   $38.30  
  Purchase #2 $174.96   3.195%   $180.55   $180.55   $180.55   $180.60  
  Purchase #3 $116.67   7.278%   $125.1612   $125.16   $125.15   $125.20  
  Purchase #4 $83.29   3.479%   $86.1877   $86.19   $86.20   $86.20  
  Purchase #5 $234.48   5.359%   $247.0458   $247.05   $247.05   $247.00  
  Purchase #6 $210.51   6.410%   $224.0037   $224.00   $224.00   $224.00  
  Purchase #7 $134.59   13.714%   $153.0477   $153.05   $153.05   $153.00  
  7 purchase totals = $990.34       $1,054.2747   $1,054.28   $1,054.30   $1,054.30