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 $57.32   7.358%   $61.5376   $61.54   $61.55   $61.50  
  Purchase #2 $141.81   10.744%   $157.0461   $157.05   $157.05   $157.00  
  Purchase #3 $156.48   13.470%   $177.5579   $177.56   $177.55   $177.60  
  Purchase #4 $57.92   9.349%   $63.3349   $63.33   $63.35   $63.30  
  Purchase #5 $43.79   6.433%   $46.607   $46.61   $46.60   $46.60  
  Purchase #6 $48.92   4.635%   $51.1874   $51.19   $51.20   $51.20  
  Purchase #7 $114.39   6.690%   $122.0427   $122.04   $122.05   $122.00  
  7 purchase totals = $620.63       $679.3136   $679.32   $679.35   $679.20