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 $152.31   8.741%   $165.6234   $165.62   $165.60   $165.60  
  Purchase #2 $59.58   5.342%   $62.7628   $62.76   $62.75   $62.80  
  Purchase #3 $182.75   8.842%   $198.9088   $198.91   $198.90   $198.90  
  Purchase #4 $10.56   8.233%   $11.4294   $11.43   $11.45   $11.40  
  Purchase #5 $222.97   4.383%   $232.7428   $232.74   $232.75   $232.70  
  Purchase #6 $249.59   8.848%   $271.6737   $271.67   $271.65   $271.70  
  Purchase #7 $213.70   5.347%   $225.1265   $225.13   $225.15   $225.10  
  7 purchase totals = $1,091.46       $1,168.2674   $1,168.26   $1,168.25   $1,168.20