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 $54.54   13.412%   $61.8549   $61.85   $61.85   $61.90  
  Purchase #2 $88.33   9.424%   $96.6542   $96.65   $96.65   $96.70  
  Purchase #3 $144.35   9.264%   $157.7226   $157.72   $157.70   $157.70  
  Purchase #4 $242.89   5.821%   $257.0286   $257.03   $257.05   $257.00  
  Purchase #5 $7.90   10.402%   $8.7218   $8.72   $8.70   $8.70  
  Purchase #6 $121.90   9.812%   $133.8608   $133.86   $133.85   $133.90  
  Purchase #7 $44.63   8.304%   $48.3361   $48.34   $48.35   $48.30  
  7 purchase totals = $704.54       $764.1790   $764.17   $764.15   $764.20