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 $91.65   13.626%   $104.1382   $104.14   $104.15   $104.10  
  Purchase #2 $149.93   12.871%   $169.2275   $169.23   $169.25   $169.20  
  Purchase #3 $198.30   5.258%   $208.7266   $208.73   $208.75   $208.70  
  Purchase #4 $167.94   6.856%   $179.454   $179.45   $179.45   $179.50  
  Purchase #5 $90.25   10.306%   $99.5512   $99.55   $99.55   $99.60  
  Purchase #6 $49.87   6.416%   $53.0697   $53.07   $53.05   $53.10  
  Purchase #7 $82.58   13.137%   $93.4285   $93.43   $93.45   $93.40  
  7 purchase totals = $830.52       $907.5957   $907.60   $907.65   $907.60