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 $236.81   9.585%   $259.5082   $259.51   $259.50   $259.50  
  Purchase #2 $201.58   11.480%   $224.7214   $224.72   $224.70   $224.70  
  Purchase #3 $202.91   11.358%   $225.9565   $225.96   $225.95   $226.00  
  Purchase #4 $6.97   6.292%   $7.4086   $7.41   $7.40   $7.40  
  Purchase #5 $58.87   5.146%   $61.8995   $61.90   $61.90   $61.90  
  Purchase #6 $177.54   12.358%   $199.4804   $199.48   $199.50   $199.50  
  Purchase #7 $242.30   10.351%   $267.3805   $267.38   $267.40   $267.40  
  7 purchase totals = $1,126.98       $1,246.3551   $1,246.36   $1,246.35   $1,246.40