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 $94.70   8.175%   $102.4417   $102.44   $102.45   $102.40  
  Purchase #2 $7.78   5.651%   $8.2196   $8.22   $8.20   $8.20  
  Purchase #3 $24.63   7.611%   $26.5046   $26.50   $26.50   $26.50  
  Purchase #4 $219.93   4.256%   $229.2902   $229.29   $229.30   $229.30  
  Purchase #5 $212.46   13.222%   $240.5515   $240.55   $240.55   $240.60  
  Purchase #6 $238.62   7.723%   $257.0486   $257.05   $257.05   $257.00  
  Purchase #7 $57.75   5.508%   $60.9309   $60.93   $60.95   $60.90  
  7 purchase totals = $855.87       $924.9871   $924.98   $925.00   $924.90