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 $171.38   13.366%   $194.2867   $194.29   $194.30   $194.30  
  Purchase #2 $33.73   6.281%   $35.8486   $35.85   $35.85   $35.80  
  Purchase #3 $96.69   3.646%   $100.2153   $100.22   $100.20   $100.20  
  Purchase #4 $118.83   12.809%   $134.0509   $134.05   $134.05   $134.10  
  Purchase #5 $88.80   12.162%   $99.5999   $99.60   $99.60   $99.60  
  Purchase #6 $106.71   8.701%   $115.9948   $115.99   $116.00   $116.00  
  Purchase #7 $195.62   11.126%   $217.3847   $217.38   $217.40   $217.40  
  7 purchase totals = $811.76       $897.3809   $897.38   $897.40   $897.40