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 $76.27   11.619%   $85.1318   $85.13   $85.15   $85.10  
  Purchase #2 $228.37   13.417%   $259.0104   $259.01   $259.00   $259.00  
  Purchase #3 $172.83   11.166%   $192.1282   $192.13   $192.15   $192.10  
  Purchase #4 $71.98   6.563%   $76.704   $76.70   $76.70   $76.70  
  Purchase #5 $250.45   9.662%   $274.6485   $274.65   $274.65   $274.60  
  Purchase #6 $153.73   7.830%   $165.7671   $165.77   $165.75   $165.80  
  Purchase #7 $59.78   7.439%   $64.227   $64.23   $64.25   $64.20  
  7 purchase totals = $1,013.41       $1,117.6170   $1,117.62   $1,117.65   $1,117.50