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 $153.84   7.582%   $165.5041   $165.50   $165.50   $165.50  
  Purchase #2 $166.57   4.262%   $173.6692   $173.67   $173.65   $173.70  
  Purchase #3 $63.42   5.188%   $66.7102   $66.71   $66.70   $66.70  
  Purchase #4 $36.93   5.569%   $38.9866   $38.99   $39.00   $39.00  
  Purchase #5 $249.83   10.457%   $275.9547   $275.95   $275.95   $276.00  
  Purchase #6 $88.64   7.493%   $95.2818   $95.28   $95.30   $95.30  
  Purchase #7 $95.81   13.701%   $108.9369   $108.94   $108.95   $108.90  
  7 purchase totals = $855.04       $925.0435   $925.04   $925.05   $925.10