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 $52.60   12.531%   $59.1913   $59.19   $59.20   $59.20  
  Purchase #2 $156.89   11.562%   $175.0296   $175.03   $175.05   $175.00  
  Purchase #3 $236.93   10.442%   $261.6702   $261.67   $261.65   $261.70  
  Purchase #4 $137.82   3.485%   $142.623   $142.62   $142.60   $142.60  
  Purchase #5 $247.97   10.583%   $274.2127   $274.21   $274.20   $274.20  
  Purchase #6 $120.71   7.840%   $130.1737   $130.17   $130.15   $130.20  
  Purchase #7 $133.95   9.811%   $147.0918   $147.09   $147.10   $147.10  
  7 purchase totals = $1,086.87       $1,189.9923   $1,189.98   $1,189.95   $1,190.00