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 $147.62   13.836%   $168.0447   $168.04   $168.05   $168.00  
  Purchase #2 $94.95   10.520%   $104.9387   $104.94   $104.95   $104.90  
  Purchase #3 $52.43   8.309%   $56.7864   $56.79   $56.80   $56.80  
  Purchase #4 $169.32   4.365%   $176.7108   $176.71   $176.70   $176.70  
  Purchase #5 $187.73   5.689%   $198.41   $198.41   $198.40   $198.40  
  Purchase #6 $65.38   13.195%   $74.0069   $74.01   $74.00   $74.00  
  Purchase #7 $157.41   3.417%   $162.7887   $162.79   $162.80   $162.80  
  7 purchase totals = $874.84       $941.6862   $941.69   $941.70   $941.60