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 $247.31   11.841%   $276.594   $276.59   $276.60   $276.60  
  Purchase #2 $177.68   5.623%   $187.6709   $187.67   $187.65   $187.70  
  Purchase #3 $56.79   9.231%   $62.0323   $62.03   $62.05   $62.00  
  Purchase #4 $112.68   12.676%   $126.9633   $126.96   $126.95   $127.00  
  Purchase #5 $8.73   7.272%   $9.3648   $9.36   $9.35   $9.40  
  Purchase #6 $177.54   10.168%   $195.5923   $195.59   $195.60   $195.60  
  Purchase #7 $162.27   3.624%   $168.1507   $168.15   $168.15   $168.20  
  7 purchase totals = $943.00       $1,026.3683   $1,026.35   $1,026.35   $1,026.50