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 $90.66   8.813%   $98.6499   $98.65   $98.65   $98.60  
  Purchase #2 $89.50   13.751%   $101.8071   $101.81   $101.80   $101.80  
  Purchase #3 $160.66   6.751%   $171.5062   $171.51   $171.50   $171.50  
  Purchase #4 $234.85   3.483%   $243.0298   $243.03   $243.05   $243.00  
  Purchase #5 $43.94   8.728%   $47.7751   $47.78   $47.80   $47.80  
  Purchase #6 $250.99   3.729%   $260.3494   $260.35   $260.35   $260.30  
  Purchase #7 $234.62   10.441%   $259.1167   $259.12   $259.10   $259.10  
  7 purchase totals = $1,105.22       $1,182.2342   $1,182.25   $1,182.25   $1,182.10