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 $112.49   6.140%   $119.3969   $119.40   $119.40   $119.40  
  Purchase #2 $215.92   11.874%   $241.5583   $241.56   $241.55   $241.60  
  Purchase #3 $239.28   10.814%   $265.1557   $265.16   $265.15   $265.20  
  Purchase #4 $242.66   6.277%   $257.8918   $257.89   $257.90   $257.90  
  Purchase #5 $155.93   8.112%   $168.579   $168.58   $168.60   $168.60  
  Purchase #6 $170.98   10.444%   $188.8372   $188.84   $188.85   $188.80  
  Purchase #7 $23.98   9.620%   $26.2869   $26.29   $26.30   $26.30  
  7 purchase totals = $1,161.24       $1,267.7058   $1,267.72   $1,267.75   $1,267.80