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 $61.59   7.438%   $66.1711   $66.17   $66.15   $66.20  
  Purchase #2 $131.26   8.445%   $142.3449   $142.34   $142.35   $142.30  
  Purchase #3 $104.59   3.293%   $108.0341   $108.03   $108.05   $108.00  
  Purchase #4 $164.70   9.412%   $180.2016   $180.20   $180.20   $180.20  
  Purchase #5 $168.57   6.504%   $179.5338   $179.53   $179.55   $179.50  
  Purchase #6 $234.60   13.845%   $267.0804   $267.08   $267.10   $267.10  
  Purchase #7 $109.43   6.412%   $116.4467   $116.45   $116.45   $116.40  
  7 purchase totals = $974.74       $1,059.8126   $1,059.80   $1,059.85   $1,059.70