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 $208.97   11.289%   $232.5606   $232.56   $232.55   $232.60  
  Purchase #2 $244.48   6.679%   $260.8088   $260.81   $260.80   $260.80  
  Purchase #3 $113.58   10.391%   $125.3821   $125.38   $125.40   $125.40  
  Purchase #4 $73.77   5.569%   $77.8783   $77.88   $77.90   $77.90  
  Purchase #5 $240.58   8.224%   $260.3653   $260.37   $260.35   $260.40  
  Purchase #6 $48.89   12.135%   $54.8228   $54.82   $54.80   $54.80  
  Purchase #7 $93.59   11.670%   $104.512   $104.51   $104.50   $104.50  
  7 purchase totals = $1,023.86       $1,116.3299   $1,116.33   $1,116.30   $1,116.40