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 $221.45   6.723%   $236.3381   $236.34   $236.35   $236.30  
  Purchase #2 $54.95   9.560%   $60.2032   $60.20   $60.20   $60.20  
  Purchase #3 $138.49   4.242%   $144.3647   $144.36   $144.35   $144.40  
  Purchase #4 $217.42   6.333%   $231.1892   $231.19   $231.20   $231.20  
  Purchase #5 $42.86   6.303%   $45.5615   $45.56   $45.55   $45.60  
  Purchase #6 $196.96   7.620%   $211.9684   $211.97   $211.95   $212.00  
  Purchase #7 $95.28   8.549%   $103.4255   $103.43   $103.45   $103.40  
  7 purchase totals = $967.41       $1,033.0506   $1,033.05   $1,033.05   $1,033.10