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 $45.55   7.468%   $48.9517   $48.95   $48.95   $49.00  
  Purchase #2 $94.76   9.364%   $103.6333   $103.63   $103.65   $103.60  
  Purchase #3 $127.48   5.376%   $134.3333   $134.33   $134.35   $134.30  
  Purchase #4 $235.41   6.414%   $250.5092   $250.51   $250.50   $250.50  
  Purchase #5 $249.67   3.834%   $259.2423   $259.24   $259.25   $259.20  
  Purchase #6 $95.46   11.645%   $106.5763   $106.58   $106.60   $106.60  
  Purchase #7 $98.69   11.419%   $109.9594   $109.96   $109.95   $110.00  
  7 purchase totals = $947.02       $1,013.2055   $1,013.20   $1,013.25   $1,013.20