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 $56.65   11.804%   $63.337   $63.34   $63.35   $63.30  
  Purchase #2 $74.71   10.468%   $82.5306   $82.53   $82.55   $82.50  
  Purchase #3 $83.62   12.509%   $94.08   $94.08   $94.10   $94.10  
  Purchase #4 $20.89   8.562%   $22.6786   $22.68   $22.70   $22.70  
  Purchase #5 $156.89   13.353%   $177.8395   $177.84   $177.85   $177.80  
  Purchase #6 $242.95   13.379%   $275.4543   $275.45   $275.45   $275.50  
  Purchase #7 $55.84   7.278%   $59.904   $59.90   $59.90   $59.90  
  7 purchase totals = $691.55       $775.8240   $775.82   $775.90   $775.80