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 $195.88   4.721%   $205.1275   $205.13   $205.15   $205.10  
  Purchase #2 $116.65   3.407%   $120.6243   $120.62   $120.60   $120.60  
  Purchase #3 $29.26   11.798%   $32.7121   $32.71   $32.70   $32.70  
  Purchase #4 $178.89   5.371%   $188.4982   $188.50   $188.50   $188.50  
  Purchase #5 $231.95   11.586%   $258.8237   $258.82   $258.80   $258.80  
  Purchase #6 $145.88   3.778%   $151.3913   $151.39   $151.40   $151.40  
  Purchase #7 $67.34   3.343%   $69.5912   $69.59   $69.60   $69.60  
  7 purchase totals = $965.85       $1,026.7683   $1,026.76   $1,026.75   $1,026.70