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 $62.84   4.611%   $65.7376   $65.74   $65.75   $65.70  
  Purchase #2 $92.29   11.287%   $102.7068   $102.71   $102.70   $102.70  
  Purchase #3 $24.60   6.795%   $26.2716   $26.27   $26.25   $26.30  
  Purchase #4 $66.80   7.234%   $71.6323   $71.63   $71.65   $71.60  
  Purchase #5 $9.42   6.488%   $10.0312   $10.03   $10.05   $10.00  
  Purchase #6 $80.59   5.832%   $85.29   $85.29   $85.30   $85.30  
  Purchase #7 $201.38   9.611%   $220.7346   $220.73   $220.75   $220.70  
  7 purchase totals = $537.92       $582.4041   $582.40   $582.45   $582.30