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 $32.31   13.453%   $36.6567   $36.66   $36.65   $36.70  
  Purchase #2 $199.72   3.138%   $205.9872   $205.99   $206.00   $206.00  
  Purchase #3 $16.61   9.534%   $18.1936   $18.19   $18.20   $18.20  
  Purchase #4 $45.56   6.194%   $48.382   $48.38   $48.40   $48.40  
  Purchase #5 $104.65   13.145%   $118.4062   $118.41   $118.40   $118.40  
  Purchase #6 $11.30   6.692%   $12.0562   $12.06   $12.05   $12.10  
  Purchase #7 $87.93   8.455%   $95.3645   $95.36   $95.35   $95.40  
  7 purchase totals = $498.08       $535.0464   $535.05   $535.05   $535.20