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 $216.86   11.135%   $241.0074   $241.01   $241.00   $241.00  
  Purchase #2 $31.97   13.641%   $36.331   $36.33   $36.35   $36.30  
  Purchase #3 $38.66   10.133%   $42.5774   $42.58   $42.60   $42.60  
  Purchase #4 $121.37   13.258%   $137.4612   $137.46   $137.45   $137.50  
  Purchase #5 $147.36   3.512%   $152.5353   $152.54   $152.55   $152.50  
  Purchase #6 $52.54   10.794%   $58.2112   $58.21   $58.20   $58.20  
  Purchase #7 $222.91   11.833%   $249.2869   $249.29   $249.30   $249.30  
  7 purchase totals = $831.67       $917.4104   $917.42   $917.45   $917.40