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 $207.69   10.196%   $228.8661   $228.87   $228.85   $228.90  
  Purchase #2 $158.45   11.439%   $176.5751   $176.58   $176.60   $176.60  
  Purchase #3 $236.94   5.664%   $250.3603   $250.36   $250.35   $250.40  
  Purchase #4 $54.84   8.826%   $59.6802   $59.68   $59.70   $59.70  
  Purchase #5 $9.69   6.510%   $10.3208   $10.32   $10.30   $10.30  
  Purchase #6 $165.94   4.457%   $173.3359   $173.34   $173.35   $173.30  
  Purchase #7 $47.33   8.314%   $51.265   $51.27   $51.25   $51.30  
  7 purchase totals = $880.88       $950.4034   $950.42   $950.40   $950.50