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 $79.92   11.273%   $88.9294   $88.93   $88.95   $88.90  
  Purchase #2 $249.28   3.445%   $257.8677   $257.87   $257.85   $257.90  
  Purchase #3 $45.99   13.836%   $52.3532   $52.35   $52.35   $52.40  
  Purchase #4 $53.38   8.439%   $57.8847   $57.88   $57.90   $57.90  
  Purchase #5 $43.71   3.649%   $45.305   $45.31   $45.30   $45.30  
  Purchase #6 $43.95   11.390%   $48.9559   $48.96   $48.95   $49.00  
  Purchase #7 $219.64   11.640%   $245.2061   $245.21   $245.20   $245.20  
  7 purchase totals = $735.87       $796.5020   $796.51   $796.50   $796.60