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 $90.71   3.242%   $93.6508   $93.65   $93.65   $93.70  
  Purchase #2 $228.73   7.172%   $245.1345   $245.13   $245.15   $245.10  
  Purchase #3 $24.96   7.455%   $26.8208   $26.82   $26.80   $26.80  
  Purchase #4 $211.60   6.648%   $225.6672   $225.67   $225.65   $225.70  
  Purchase #5 $136.93   8.405%   $148.439   $148.44   $148.45   $148.40  
  Purchase #6 $103.49   8.141%   $111.9151   $111.92   $111.90   $111.90  
  Purchase #7 $213.48   10.578%   $236.0619   $236.06   $236.05   $236.10  
  7 purchase totals = $1,009.90       $1,087.6893   $1,087.69   $1,087.65   $1,087.70