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 $189.52   6.768%   $202.3467   $202.35   $202.35   $202.30  
  Purchase #2 $93.84   10.110%   $103.3272   $103.33   $103.35   $103.30  
  Purchase #3 $246.37   5.663%   $260.3219   $260.32   $260.30   $260.30  
  Purchase #4 $111.57   6.867%   $119.2315   $119.23   $119.25   $119.20  
  Purchase #5 $187.40   12.537%   $210.8943   $210.89   $210.90   $210.90  
  Purchase #6 $213.48   8.432%   $231.4806   $231.48   $231.50   $231.50  
  Purchase #7 $153.71   9.768%   $168.7244   $168.72   $168.70   $168.70  
  7 purchase totals = $1,195.89       $1,296.3266   $1,296.32   $1,296.35   $1,296.20