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 $81.79   5.217%   $86.057   $86.06   $86.05   $86.10  
  Purchase #2 $70.88   3.554%   $73.3991   $73.40   $73.40   $73.40  
  Purchase #3 $143.41   4.318%   $149.6024   $149.60   $149.60   $149.60  
  Purchase #4 $209.42   9.266%   $228.8249   $228.82   $228.80   $228.80  
  Purchase #5 $232.58   5.446%   $245.2463   $245.25   $245.25   $245.20  
  Purchase #6 $145.81   11.316%   $162.3099   $162.31   $162.30   $162.30  
  Purchase #7 $101.84   12.351%   $114.4183   $114.42   $114.40   $114.40  
  7 purchase totals = $985.73       $1,059.8579   $1,059.86   $1,059.80   $1,059.80