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 $63.54   8.535%   $68.9631   $68.96   $68.95   $69.00  
  Purchase #2 $102.66   3.806%   $106.5672   $106.57   $106.55   $106.60  
  Purchase #3 $213.90   12.156%   $239.9017   $239.90   $239.90   $239.90  
  Purchase #4 $203.29   4.576%   $212.5926   $212.59   $212.60   $212.60  
  Purchase #5 $62.41   5.123%   $65.6073   $65.61   $65.60   $65.60  
  Purchase #6 $114.50   10.223%   $126.2053   $126.21   $126.20   $126.20  
  Purchase #7 $89.94   6.113%   $95.438   $95.44   $95.45   $95.40  
  7 purchase totals = $850.24       $915.2752   $915.28   $915.25   $915.30