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 $56.61   5.365%   $59.6471   $59.65   $59.65   $59.60  
  Purchase #2 $230.31   13.277%   $260.8883   $260.89   $260.90   $260.90  
  Purchase #3 $132.70   12.570%   $149.3804   $149.38   $149.40   $149.40  
  Purchase #4 $125.34   8.422%   $135.8961   $135.90   $135.90   $135.90  
  Purchase #5 $25.95   5.477%   $27.3713   $27.37   $27.35   $27.40  
  Purchase #6 $204.92   9.808%   $225.0186   $225.02   $225.00   $225.00  
  Purchase #7 $207.53   5.866%   $219.7037   $219.70   $219.70   $219.70  
  7 purchase totals = $983.36       $1,077.9055   $1,077.91   $1,077.90   $1,077.90