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 $247.71   5.863%   $262.2332   $262.23   $262.25   $262.20  
  Purchase #2 $34.69   7.644%   $37.3417   $37.34   $37.35   $37.30  
  Purchase #3 $225.50   12.842%   $254.4587   $254.46   $254.45   $254.50  
  Purchase #4 $141.88   13.697%   $161.3133   $161.31   $161.30   $161.30  
  Purchase #5 $77.28   9.633%   $84.7244   $84.72   $84.70   $84.70  
  Purchase #6 $102.52   10.253%   $113.0314   $113.03   $113.05   $113.00  
  Purchase #7 $67.77   5.272%   $71.3428   $71.34   $71.35   $71.30  
  7 purchase totals = $897.35       $984.4455   $984.43   $984.45   $984.30