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 $246.82   11.691%   $275.6757   $275.68   $275.70   $275.70  
  Purchase #2 $21.57   12.548%   $24.2766   $24.28   $24.30   $24.30  
  Purchase #3 $91.80   12.316%   $103.1061   $103.11   $103.10   $103.10  
  Purchase #4 $20.29   7.730%   $21.8584   $21.86   $21.85   $21.90  
  Purchase #5 $156.54   6.347%   $166.4756   $166.48   $166.50   $166.50  
  Purchase #6 $173.36   7.329%   $186.0656   $186.07   $186.05   $186.10  
  Purchase #7 $112.39   4.822%   $117.8094   $117.81   $117.80   $117.80  
  7 purchase totals = $822.77       $895.2674   $895.29   $895.30   $895.40