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 $60.93   13.651%   $69.2476   $69.25   $69.25   $69.20  
  Purchase #2 $110.25   3.614%   $114.2344   $114.23   $114.25   $114.20  
  Purchase #3 $14.51   11.135%   $16.1257   $16.13   $16.15   $16.10  
  Purchase #4 $55.72   6.870%   $59.548   $59.55   $59.55   $59.50  
  Purchase #5 $194.30   5.651%   $205.2799   $205.28   $205.30   $205.30  
  Purchase #6 $76.36   5.666%   $80.6866   $80.69   $80.70   $80.70  
  Purchase #7 $54.96   6.460%   $58.5104   $58.51   $58.50   $58.50  
  7 purchase totals = $567.03       $603.6326   $603.64   $603.70   $603.50