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 $36.87   12.217%   $41.3744   $41.37   $41.35   $41.40  
  Purchase #2 $120.91   8.581%   $131.2853   $131.29   $131.30   $131.30  
  Purchase #3 $193.68   10.728%   $214.458   $214.46   $214.45   $214.50  
  Purchase #4 $188.31   5.784%   $199.2019   $199.20   $199.20   $199.20  
  Purchase #5 $182.99   10.567%   $202.3266   $202.33   $202.35   $202.30  
  Purchase #6 $138.54   13.203%   $156.8314   $156.83   $156.85   $156.80  
  Purchase #7 $17.50   5.283%   $18.4245   $18.42   $18.40   $18.40  
  7 purchase totals = $878.80       $963.9021   $963.90   $963.90   $963.90