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 $206.43   12.509%   $232.2523   $232.25   $232.25   $232.30  
  Purchase #2 $62.98   13.593%   $71.5409   $71.54   $71.55   $71.50  
  Purchase #3 $51.53   7.621%   $55.4571   $55.46   $55.45   $55.50  
  Purchase #4 $29.57   11.387%   $32.9371   $32.94   $32.95   $32.90  
  Purchase #5 $242.66   7.171%   $260.0611   $260.06   $260.05   $260.10  
  Purchase #6 $220.68   12.467%   $248.1922   $248.19   $248.20   $248.20  
  Purchase #7 $243.36   4.166%   $253.4984   $253.50   $253.50   $253.50  
  7 purchase totals = $1,057.21       $1,153.9391   $1,153.94   $1,153.95   $1,154.00