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 $78.62   8.359%   $85.1918   $85.19   $85.20   $85.20  
  Purchase #2 $168.99   3.198%   $174.3943   $174.39   $174.40   $174.40  
  Purchase #3 $241.28   8.587%   $261.9987   $262.00   $262.00   $262.00  
  Purchase #4 $19.65   5.723%   $20.7746   $20.77   $20.75   $20.80  
  Purchase #5 $178.40   8.413%   $193.4088   $193.41   $193.40   $193.40  
  Purchase #6 $141.85   4.515%   $148.2545   $148.25   $148.25   $148.30  
  Purchase #7 $167.86   11.195%   $186.6519   $186.65   $186.65   $186.70  
  7 purchase totals = $996.65       $1,070.6746   $1,070.66   $1,070.65   $1,070.80