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 $185.36   4.803%   $194.2628   $194.26   $194.25   $194.30  
  Purchase #2 $227.65   3.164%   $234.8528   $234.85   $234.85   $234.90  
  Purchase #3 $179.85   5.841%   $190.355   $190.36   $190.35   $190.40  
  Purchase #4 $175.87   5.394%   $185.3564   $185.36   $185.35   $185.40  
  Purchase #5 $248.44   8.175%   $268.75   $268.75   $268.75   $268.80  
  Purchase #6 $93.78   12.332%   $105.3449   $105.34   $105.35   $105.30  
  Purchase #7 $67.42   11.416%   $75.1167   $75.12   $75.10   $75.10  
  7 purchase totals = $1,178.37       $1,254.0386   $1,254.04   $1,254.00   $1,254.20