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 $92.44   12.664%   $104.1466   $104.15   $104.15   $104.10  
  Purchase #2 $26.29   5.258%   $27.6723   $27.67   $27.65   $27.70  
  Purchase #3 $10.84   9.308%   $11.849   $11.85   $11.85   $11.80  
  Purchase #4 $153.89   7.230%   $165.0162   $165.02   $165.00   $165.00  
  Purchase #5 $143.28   4.598%   $149.868   $149.87   $149.85   $149.90  
  Purchase #6 $177.70   4.686%   $186.027   $186.03   $186.05   $186.00  
  Purchase #7 $93.87   3.718%   $97.3601   $97.36   $97.35   $97.40  
  7 purchase totals = $698.31       $741.9392   $741.95   $741.90   $741.90