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 $62.80   6.319%   $66.7683   $66.77   $66.75   $66.80  
  Purchase #2 $74.95   9.547%   $82.1055   $82.11   $82.10   $82.10  
  Purchase #3 $117.96   6.460%   $125.5802   $125.58   $125.60   $125.60  
  Purchase #4 $175.93   12.712%   $198.2942   $198.29   $198.30   $198.30  
  Purchase #5 $246.85   6.532%   $262.9742   $262.97   $262.95   $263.00  
  Purchase #6 $200.83   6.229%   $213.3397   $213.34   $213.35   $213.30  
  Purchase #7 $82.77   11.662%   $92.4226   $92.42   $92.40   $92.40  
  7 purchase totals = $962.09       $1,041.4847   $1,041.48   $1,041.45   $1,041.50