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 $160.60   4.393%   $167.6552   $167.66   $167.65   $167.70  
  Purchase #2 $90.86   4.340%   $94.8033   $94.80   $94.80   $94.80  
  Purchase #3 $118.75   5.871%   $125.7218   $125.72   $125.70   $125.70  
  Purchase #4 $205.31   9.837%   $225.5063   $225.51   $225.50   $225.50  
  Purchase #5 $15.85   11.861%   $17.73   $17.73   $17.75   $17.70  
  Purchase #6 $143.75   10.258%   $158.4959   $158.50   $158.50   $158.50  
  Purchase #7 $43.79   9.129%   $47.7876   $47.79   $47.80   $47.80  
  7 purchase totals = $778.91       $837.7001   $837.71   $837.70   $837.70