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 $34.61   5.759%   $36.6032   $36.60   $36.60   $36.60  
  Purchase #2 $165.43   13.697%   $188.0889   $188.09   $188.10   $188.10  
  Purchase #3 $94.38   11.117%   $104.8722   $104.87   $104.85   $104.90  
  Purchase #4 $101.95   13.585%   $115.7999   $115.80   $115.80   $115.80  
  Purchase #5 $96.81   5.658%   $102.2875   $102.29   $102.30   $102.30  
  Purchase #6 $194.71   3.313%   $201.1607   $201.16   $201.15   $201.20  
  Purchase #7 $135.55   8.495%   $147.065   $147.07   $147.05   $147.10  
  7 purchase totals = $823.44       $895.8774   $895.88   $895.85   $896.00