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 $239.62   11.682%   $267.6124   $267.61   $267.60   $267.60  
  Purchase #2 $105.69   12.252%   $118.6391   $118.64   $118.65   $118.60  
  Purchase #3 $121.54   7.469%   $130.6178   $130.62   $130.60   $130.60  
  Purchase #4 $31.73   6.698%   $33.8553   $33.86   $33.85   $33.90  
  Purchase #5 $54.99   5.769%   $58.1624   $58.16   $58.15   $58.20  
  Purchase #6 $150.84   13.170%   $170.7056   $170.71   $170.70   $170.70  
  Purchase #7 $28.43   5.595%   $30.0207   $30.02   $30.00   $30.00  
  7 purchase totals = $732.84       $809.6133   $809.62   $809.55   $809.60