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 $249.29   10.726%   $276.0288   $276.03   $276.05   $276.00  
  Purchase #2 $96.97   7.601%   $104.3407   $104.34   $104.35   $104.30  
  Purchase #3 $185.84   12.747%   $209.529   $209.53   $209.55   $209.50  
  Purchase #4 $131.83   11.629%   $147.1605   $147.16   $147.15   $147.20  
  Purchase #5 $129.25   5.486%   $136.3407   $136.34   $136.35   $136.30  
  Purchase #6 $200.80   4.248%   $209.33   $209.33   $209.35   $209.30  
  Purchase #7 $48.95   4.751%   $51.2756   $51.28   $51.30   $51.30  
  7 purchase totals = $1,042.93       $1,134.0053   $1,134.01   $1,134.10   $1,133.90