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 $41.91   6.545%   $44.653   $44.65   $44.65   $44.70  
  Purchase #2 $156.81   4.582%   $163.995   $164.00   $164.00   $164.00  
  Purchase #3 $74.67   6.274%   $79.3548   $79.35   $79.35   $79.40  
  Purchase #4 $121.55   6.224%   $129.1153   $129.12   $129.10   $129.10  
  Purchase #5 $217.57   12.726%   $245.258   $245.26   $245.25   $245.30  
  Purchase #6 $106.41   9.573%   $116.5966   $116.60   $116.60   $116.60  
  Purchase #7 $13.92   7.779%   $15.0028   $15.00   $15.00   $15.00  
  7 purchase totals = $732.84       $793.9755   $793.98   $793.95   $794.10