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 $193.77   9.726%   $212.6161   $212.62   $212.60   $212.60  
  Purchase #2 $235.75   4.200%   $245.6515   $245.65   $245.65   $245.70  
  Purchase #3 $47.76   12.107%   $53.5423   $53.54   $53.55   $53.50  
  Purchase #4 $27.28   12.794%   $30.7702   $30.77   $30.75   $30.80  
  Purchase #5 $46.89   8.869%   $51.0487   $51.05   $51.05   $51.00  
  Purchase #6 $185.60   11.854%   $207.601   $207.60   $207.60   $207.60  
  Purchase #7 $147.74   6.234%   $156.9501   $156.95   $156.95   $157.00  
  7 purchase totals = $884.79       $958.1799   $958.18   $958.15   $958.20