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 $24.26   3.806%   $25.1833   $25.18   $25.20   $25.20  
  Purchase #2 $188.58   13.799%   $214.6022   $214.60   $214.60   $214.60  
  Purchase #3 $247.89   7.760%   $267.1263   $267.13   $267.15   $267.10  
  Purchase #4 $202.51   12.270%   $227.358   $227.36   $227.35   $227.40  
  Purchase #5 $238.30   9.455%   $260.8313   $260.83   $260.85   $260.80  
  Purchase #6 $223.97   5.692%   $236.7184   $236.72   $236.70   $236.70  
  Purchase #7 $29.59   3.861%   $30.7325   $30.73   $30.75   $30.70  
  7 purchase totals = $1,155.10       $1,262.5520   $1,262.55   $1,262.60   $1,262.50