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 $208.91   6.837%   $223.1932   $223.19   $223.20   $223.20  
  Purchase #2 $33.29   4.230%   $34.6982   $34.70   $34.70   $34.70  
  Purchase #3 $217.38   4.165%   $226.4339   $226.43   $226.45   $226.40  
  Purchase #4 $15.35   3.672%   $15.9137   $15.91   $15.90   $15.90  
  Purchase #5 $68.44   6.797%   $73.0919   $73.09   $73.10   $73.10  
  Purchase #6 $29.89   6.803%   $31.9234   $31.92   $31.90   $31.90  
  Purchase #7 $218.97   4.724%   $229.3141   $229.31   $229.30   $229.30  
  7 purchase totals = $792.23       $834.5684   $834.55   $834.55   $834.50