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 $22.84   7.184%   $24.4808   $24.48   $24.50   $24.50  
  Purchase #2 $241.25   11.219%   $268.3158   $268.32   $268.30   $268.30  
  Purchase #3 $93.55   3.818%   $97.1217   $97.12   $97.10   $97.10  
  Purchase #4 $248.25   11.449%   $276.6721   $276.67   $276.65   $276.70  
  Purchase #5 $39.51   10.587%   $43.6929   $43.69   $43.70   $43.70  
  Purchase #6 $7.78   6.478%   $8.284   $8.28   $8.30   $8.30  
  Purchase #7 $215.68   10.478%   $238.279   $238.28   $238.30   $238.30  
  7 purchase totals = $868.86       $956.8463   $956.84   $956.85   $956.90