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 $96.43   8.112%   $104.2524   $104.25   $104.25   $104.30  
  Purchase #2 $84.36   12.798%   $95.1564   $95.16   $95.15   $95.20  
  Purchase #3 $157.85   4.758%   $165.3605   $165.36   $165.35   $165.40  
  Purchase #4 $240.64   9.211%   $262.8054   $262.81   $262.80   $262.80  
  Purchase #5 $85.84   13.219%   $97.1872   $97.19   $97.20   $97.20  
  Purchase #6 $87.63   7.866%   $94.523   $94.52   $94.50   $94.50  
  Purchase #7 $197.45   3.451%   $204.264   $204.26   $204.25   $204.30  
  7 purchase totals = $950.20       $1,023.5489   $1,023.55   $1,023.50   $1,023.70