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 $172.26   5.766%   $182.1925   $182.19   $182.20   $182.20  
  Purchase #2 $116.88   7.819%   $126.0188   $126.02   $126.00   $126.00  
  Purchase #3 $31.51   4.742%   $33.0042   $33.00   $33.00   $33.00  
  Purchase #4 $55.32   8.658%   $60.1096   $60.11   $60.10   $60.10  
  Purchase #5 $112.36   4.318%   $117.2117   $117.21   $117.20   $117.20  
  Purchase #6 $70.26   8.387%   $76.1527   $76.15   $76.15   $76.20  
  Purchase #7 $176.27   8.384%   $191.0485   $191.05   $191.05   $191.00  
  7 purchase totals = $734.86       $785.7380   $785.73   $785.70   $785.70