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 $224.97   13.784%   $255.9799   $255.98   $256.00   $256.00  
  Purchase #2 $174.63   11.363%   $194.4732   $194.47   $194.45   $194.50  
  Purchase #3 $222.73   8.127%   $240.8313   $240.83   $240.85   $240.80  
  Purchase #4 $178.64   5.131%   $187.806   $187.81   $187.80   $187.80  
  Purchase #5 $229.57   7.871%   $247.6395   $247.64   $247.65   $247.60  
  Purchase #6 $160.95   4.196%   $167.7035   $167.70   $167.70   $167.70  
  Purchase #7 $207.25   11.265%   $230.5967   $230.60   $230.60   $230.60  
  7 purchase totals = $1,398.74       $1,525.0301   $1,525.03   $1,525.05   $1,525.00