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 $245.79   5.773%   $259.9795   $259.98   $260.00   $260.00  
  Purchase #2 $185.72   9.154%   $202.7208   $202.72   $202.70   $202.70  
  Purchase #3 $101.47   11.461%   $113.0995   $113.10   $113.10   $113.10  
  Purchase #4 $228.74   10.399%   $252.5267   $252.53   $252.55   $252.50  
  Purchase #5 $218.25   5.458%   $230.1621   $230.16   $230.15   $230.20  
  Purchase #6 $146.96   7.259%   $157.6278   $157.63   $157.65   $157.60  
  Purchase #7 $143.97   4.565%   $150.5422   $150.54   $150.55   $150.50  
  7 purchase totals = $1,270.90       $1,366.6586   $1,366.66   $1,366.70   $1,366.60