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 $69.42   13.297%   $78.6508   $78.65   $78.65   $78.70  
  Purchase #2 $193.26   5.862%   $204.5889   $204.59   $204.60   $204.60  
  Purchase #3 $94.33   7.610%   $101.5085   $101.51   $101.50   $101.50  
  Purchase #4 $104.74   9.420%   $114.6065   $114.61   $114.60   $114.60  
  Purchase #5 $113.94   7.598%   $122.5972   $122.60   $122.60   $122.60  
  Purchase #6 $143.58   8.349%   $155.5675   $155.57   $155.55   $155.60  
  Purchase #7 $143.81   8.507%   $156.0439   $156.04   $156.05   $156.00  
  7 purchase totals = $863.08       $933.5633   $933.57   $933.55   $933.60