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 $47.78   4.700%   $50.0257   $50.03   $50.05   $50.00  
  Purchase #2 $145.72   13.869%   $165.9299   $165.93   $165.95   $165.90  
  Purchase #3 $149.43   10.176%   $164.636   $164.64   $164.65   $164.60  
  Purchase #4 $236.49   7.743%   $254.8014   $254.80   $254.80   $254.80  
  Purchase #5 $174.54   8.869%   $190.02   $190.02   $190.00   $190.00  
  Purchase #6 $161.55   8.308%   $174.9716   $174.97   $174.95   $175.00  
  Purchase #7 $246.36   5.420%   $259.7127   $259.71   $259.70   $259.70  
  7 purchase totals = $1,161.87       $1,260.0973   $1,260.10   $1,260.10   $1,260.00