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 $45.86   4.780%   $48.0521   $48.05   $48.05   $48.10  
  Purchase #2 $66.41   11.135%   $73.8048   $73.80   $73.80   $73.80  
  Purchase #3 $22.37   9.183%   $24.4242   $24.42   $24.40   $24.40  
  Purchase #4 $196.86   10.131%   $216.8039   $216.80   $216.80   $216.80  
  Purchase #5 $119.57   13.447%   $135.6486   $135.65   $135.65   $135.60  
  Purchase #6 $196.47   4.267%   $204.8534   $204.85   $204.85   $204.90  
  Purchase #7 $15.63   4.212%   $16.2883   $16.29   $16.30   $16.30  
  7 purchase totals = $663.17       $719.8753   $719.86   $719.85   $719.90