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 $246.96   7.541%   $265.5833   $265.58   $265.60   $265.60  
  Purchase #2 $223.79   7.844%   $241.3441   $241.34   $241.35   $241.30  
  Purchase #3 $126.31   3.662%   $130.9355   $130.94   $130.95   $130.90  
  Purchase #4 $112.80   12.725%   $127.1538   $127.15   $127.15   $127.20  
  Purchase #5 $117.77   6.854%   $125.842   $125.84   $125.85   $125.80  
  Purchase #6 $48.42   9.456%   $52.9986   $53.00   $53.00   $53.00  
  Purchase #7 $89.78   8.481%   $97.3942   $97.39   $97.40   $97.40  
  7 purchase totals = $965.83       $1,041.2515   $1,041.24   $1,041.30   $1,041.20