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 $40.82   3.682%   $42.323   $42.32   $42.30   $42.30  
  Purchase #2 $90.50   5.307%   $95.3028   $95.30   $95.30   $95.30  
  Purchase #3 $106.90   3.468%   $110.6073   $110.61   $110.60   $110.60  
  Purchase #4 $181.93   7.570%   $195.7021   $195.70   $195.70   $195.70  
  Purchase #5 $176.39   6.442%   $187.753   $187.75   $187.75   $187.80  
  Purchase #6 $126.63   11.685%   $141.4267   $141.43   $141.45   $141.40  
  Purchase #7 $178.96   11.841%   $200.1507   $200.15   $200.15   $200.20  
  7 purchase totals = $902.13       $973.2656   $973.26   $973.25   $973.30