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 $193.94   10.121%   $213.5687   $213.57   $213.55   $213.60  
  Purchase #2 $148.97   8.510%   $161.6473   $161.65   $161.65   $161.60  
  Purchase #3 $150.94   11.296%   $167.9902   $167.99   $168.00   $168.00  
  Purchase #4 $83.82   11.378%   $93.357   $93.36   $93.35   $93.40  
  Purchase #5 $23.41   4.126%   $24.3759   $24.38   $24.40   $24.40  
  Purchase #6 $231.65   10.181%   $255.2343   $255.23   $255.25   $255.20  
  Purchase #7 $76.32   8.162%   $82.5492   $82.55   $82.55   $82.50  
  7 purchase totals = $909.05       $998.7226   $998.73   $998.75   $998.70