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 $64.27   5.802%   $67.9989   $68.00   $68.00   $68.00  
  Purchase #2 $110.27   8.302%   $119.4246   $119.42   $119.40   $119.40  
  Purchase #3 $206.92   6.107%   $219.5566   $219.56   $219.55   $219.60  
  Purchase #4 $115.72   8.160%   $125.1628   $125.16   $125.15   $125.20  
  Purchase #5 $182.65   13.792%   $207.8411   $207.84   $207.85   $207.80  
  Purchase #6 $108.86   3.450%   $112.6157   $112.62   $112.60   $112.60  
  Purchase #7 $158.42   5.703%   $167.4547   $167.45   $167.45   $167.50  
  7 purchase totals = $947.11       $1,020.0544   $1,020.05   $1,020.00   $1,020.10