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 $238.38   9.299%   $260.547   $260.55   $260.55   $260.50  
  Purchase #2 $10.28   7.646%   $11.066   $11.07   $11.05   $11.10  
  Purchase #3 $104.64   12.283%   $117.4929   $117.49   $117.50   $117.50  
  Purchase #4 $228.74   11.250%   $254.4733   $254.47   $254.45   $254.50  
  Purchase #5 $233.91   12.247%   $262.557   $262.56   $262.55   $262.60  
  Purchase #6 $48.47   3.712%   $50.2692   $50.27   $50.25   $50.30  
  Purchase #7 $194.77   4.485%   $203.5054   $203.51   $203.50   $203.50  
  7 purchase totals = $1,059.19       $1,159.9108   $1,159.92   $1,159.85   $1,160.00