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 $206.79   12.439%   $232.5126   $232.51   $232.50   $232.50  
  Purchase #2 $85.53   12.461%   $96.1879   $96.19   $96.20   $96.20  
  Purchase #3 $63.98   12.243%   $71.8131   $71.81   $71.80   $71.80  
  Purchase #4 $119.25   6.826%   $127.39   $127.39   $127.40   $127.40  
  Purchase #5 $22.38   11.562%   $24.9676   $24.97   $24.95   $25.00  
  Purchase #6 $66.59   6.112%   $70.66   $70.66   $70.65   $70.70  
  Purchase #7 $154.85   8.295%   $167.6948   $167.69   $167.70   $167.70  
  7 purchase totals = $719.37       $791.2260   $791.22   $791.20   $791.30