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 $217.53   12.755%   $245.276   $245.28   $245.30   $245.30  
  Purchase #2 $54.96   12.259%   $61.6975   $61.70   $61.70   $61.70  
  Purchase #3 $175.78   8.465%   $190.6598   $190.66   $190.65   $190.70  
  Purchase #4 $40.59   4.351%   $42.3561   $42.36   $42.35   $42.40  
  Purchase #5 $27.81   12.444%   $31.2707   $31.27   $31.25   $31.30  
  Purchase #6 $52.65   10.283%   $58.064   $58.06   $58.05   $58.10  
  Purchase #7 $114.79   9.142%   $125.2841   $125.28   $125.30   $125.30  
  7 purchase totals = $684.11       $754.6082   $754.61   $754.60   $754.80