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 $216.57   7.733%   $233.3174   $233.32   $233.30   $233.30  
  Purchase #2 $183.62   10.834%   $203.5134   $203.51   $203.50   $203.50  
  Purchase #3 $51.86   5.450%   $54.6864   $54.69   $54.70   $54.70  
  Purchase #4 $174.63   11.157%   $194.1135   $194.11   $194.10   $194.10  
  Purchase #5 $234.25   11.260%   $260.6266   $260.63   $260.65   $260.60  
  Purchase #6 $162.80   12.710%   $183.4919   $183.49   $183.50   $183.50  
  Purchase #7 $222.83   10.232%   $245.63   $245.63   $245.65   $245.60  
  7 purchase totals = $1,246.56       $1,375.3792   $1,375.38   $1,375.40   $1,375.30