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 $136.97   10.263%   $151.0272   $151.03   $151.05   $151.00  
  Purchase #2 $246.28   3.420%   $254.7028   $254.70   $254.70   $254.70  
  Purchase #3 $64.72   3.515%   $66.9949   $66.99   $67.00   $67.00  
  Purchase #4 $100.43   11.620%   $112.1   $112.10   $112.10   $112.10  
  Purchase #5 $22.33   7.265%   $23.9523   $23.95   $23.95   $24.00  
  Purchase #6 $88.39   3.601%   $91.5729   $91.57   $91.55   $91.60  
  Purchase #7 $48.99   4.251%   $51.0726   $51.07   $51.05   $51.10  
  7 purchase totals = $708.11       $751.4227   $751.41   $751.40   $751.50