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 $15.45   3.496%   $15.9901   $15.99   $16.00   $16.00  
  Purchase #2 $128.63   13.593%   $146.1147   $146.11   $146.10   $146.10  
  Purchase #3 $114.79   3.235%   $118.5035   $118.50   $118.50   $118.50  
  Purchase #4 $6.59   9.543%   $7.2189   $7.22   $7.20   $7.20  
  Purchase #5 $28.69   3.778%   $29.7739   $29.77   $29.75   $29.80  
  Purchase #6 $155.94   11.627%   $174.0711   $174.07   $174.05   $174.10  
  Purchase #7 $169.72   8.544%   $184.2209   $184.22   $184.20   $184.20  
  7 purchase totals = $619.81       $675.8931   $675.88   $675.80   $675.90