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 $112.35   12.676%   $126.5915   $126.59   $126.60   $126.60  
  Purchase #2 $53.32   9.354%   $58.3076   $58.31   $58.30   $58.30  
  Purchase #3 $41.43   7.264%   $44.4395   $44.44   $44.45   $44.40  
  Purchase #4 $204.79   7.571%   $220.2947   $220.29   $220.30   $220.30  
  Purchase #5 $38.46   10.676%   $42.566   $42.57   $42.55   $42.60  
  Purchase #6 $239.30   3.377%   $247.3812   $247.38   $247.40   $247.40  
  Purchase #7 $165.31   12.778%   $186.4333   $186.43   $186.45   $186.40  
  7 purchase totals = $854.96       $926.0138   $926.01   $926.05   $926.00