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 $246.62   12.429%   $277.2724   $277.27   $277.25   $277.30  
  Purchase #2 $69.43   7.142%   $74.3887   $74.39   $74.40   $74.40  
  Purchase #3 $163.96   3.221%   $169.2412   $169.24   $169.25   $169.20  
  Purchase #4 $182.44   13.495%   $207.0603   $207.06   $207.05   $207.10  
  Purchase #5 $250.94   6.212%   $266.5284   $266.53   $266.55   $266.50  
  Purchase #6 $31.95   13.803%   $36.3601   $36.36   $36.35   $36.40  
  Purchase #7 $90.43   3.819%   $93.8835   $93.88   $93.90   $93.90  
  7 purchase totals = $1,035.77       $1,124.7346   $1,124.73   $1,124.75   $1,124.80