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 $41.91   5.817%   $44.3479   $44.35   $44.35   $44.30  
  Purchase #2 $86.29   13.787%   $98.1868   $98.19   $98.20   $98.20  
  Purchase #3 $229.33   11.166%   $254.937   $254.94   $254.95   $254.90  
  Purchase #4 $240.37   5.626%   $253.8932   $253.89   $253.90   $253.90  
  Purchase #5 $98.67   7.571%   $106.1403   $106.14   $106.15   $106.10  
  Purchase #6 $90.29   5.207%   $94.9914   $94.99   $95.00   $95.00  
  Purchase #7 $136.49   8.382%   $147.9306   $147.93   $147.95   $147.90  
  7 purchase totals = $923.35       $1,000.4272   $1,000.43   $1,000.50   $1,000.30