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 $245.69   8.658%   $266.9618   $266.96   $266.95   $267.00  
  Purchase #2 $157.94   4.492%   $165.0347   $165.03   $165.05   $165.00  
  Purchase #3 $164.96   4.578%   $172.5119   $172.51   $172.50   $172.50  
  Purchase #4 $109.75   12.660%   $123.6444   $123.64   $123.65   $123.60  
  Purchase #5 $186.59   5.840%   $197.4869   $197.49   $197.50   $197.50  
  Purchase #6 $16.92   5.245%   $17.8075   $17.81   $17.80   $17.80  
  Purchase #7 $87.73   5.623%   $92.6631   $92.66   $92.65   $92.70  
  7 purchase totals = $969.58       $1,036.1103   $1,036.10   $1,036.10   $1,036.10