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 $247.80   8.116%   $267.9114   $267.91   $267.90   $267.90  
  Purchase #2 $29.27   12.282%   $32.8649   $32.86   $32.85   $32.90  
  Purchase #3 $217.96   5.499%   $229.9456   $229.95   $229.95   $229.90  
  Purchase #4 $132.29   3.165%   $136.477   $136.48   $136.50   $136.50  
  Purchase #5 $190.63   10.848%   $211.3095   $211.31   $211.30   $211.30  
  Purchase #6 $171.77   12.604%   $193.4199   $193.42   $193.40   $193.40  
  Purchase #7 $74.62   8.623%   $81.0545   $81.05   $81.05   $81.10  
  7 purchase totals = $1,064.34       $1,152.9828   $1,152.98   $1,152.95   $1,153.00