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 $82.46   12.465%   $92.7386   $92.74   $92.75   $92.70  
  Purchase #2 $33.53   12.297%   $37.6532   $37.65   $37.65   $37.70  
  Purchase #3 $199.85   13.523%   $226.8757   $226.88   $226.90   $226.90  
  Purchase #4 $118.25   8.176%   $127.9181   $127.92   $127.90   $127.90  
  Purchase #5 $65.55   12.364%   $73.6546   $73.65   $73.65   $73.70  
  Purchase #6 $129.94   9.386%   $142.1362   $142.14   $142.15   $142.10  
  Purchase #7 $245.90   8.441%   $266.6564   $266.66   $266.65   $266.70  
  7 purchase totals = $875.48       $967.6328   $967.64   $967.65   $967.70