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 $242.74   8.781%   $264.055   $264.06   $264.05   $264.10  
  Purchase #2 $91.39   8.254%   $98.9333   $98.93   $98.95   $98.90  
  Purchase #3 $214.64   11.149%   $238.5702   $238.57   $238.55   $238.60  
  Purchase #4 $73.84   4.571%   $77.2152   $77.22   $77.20   $77.20  
  Purchase #5 $147.41   10.726%   $163.2212   $163.22   $163.20   $163.20  
  Purchase #6 $235.93   9.226%   $257.6969   $257.70   $257.70   $257.70  
  Purchase #7 $224.47   4.229%   $233.9628   $233.96   $233.95   $234.00  
  7 purchase totals = $1,230.42       $1,333.6546   $1,333.66   $1,333.60   $1,333.70