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 $205.96   13.320%   $233.3939   $233.39   $233.40   $233.40  
  Purchase #2 $68.41   11.444%   $76.2388   $76.24   $76.25   $76.20  
  Purchase #3 $104.62   8.653%   $113.6728   $113.67   $113.65   $113.70  
  Purchase #4 $212.60   11.476%   $236.998   $237.00   $237.00   $237.00  
  Purchase #5 $99.34   11.441%   $110.7055   $110.71   $110.70   $110.70  
  Purchase #6 $163.92   7.439%   $176.114   $176.11   $176.10   $176.10  
  Purchase #7 $234.79   6.442%   $249.9152   $249.92   $249.90   $249.90  
  7 purchase totals = $1,089.64       $1,197.0382   $1,197.04   $1,197.00   $1,197.00