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 $218.30   12.844%   $246.3385   $246.34   $246.35   $246.30  
  Purchase #2 $224.33   6.856%   $239.7101   $239.71   $239.70   $239.70  
  Purchase #3 $155.27   12.566%   $174.7812   $174.78   $174.80   $174.80  
  Purchase #4 $106.34   11.300%   $118.3564   $118.36   $118.35   $118.40  
  Purchase #5 $214.95   10.113%   $236.6879   $236.69   $236.70   $236.70  
  Purchase #6 $45.43   4.829%   $47.6238   $47.62   $47.60   $47.60  
  Purchase #7 $150.41   6.546%   $160.2558   $160.26   $160.25   $160.30  
  7 purchase totals = $1,115.03       $1,223.7537   $1,223.76   $1,223.75   $1,223.80