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 $46.34   3.307%   $47.8725   $47.87   $47.85   $47.90  
  Purchase #2 $127.91   3.534%   $132.4303   $132.43   $132.45   $132.40  
  Purchase #3 $57.91   4.759%   $60.6659   $60.67   $60.65   $60.70  
  Purchase #4 $34.73   10.219%   $38.2791   $38.28   $38.30   $38.30  
  Purchase #5 $38.61   12.497%   $43.4351   $43.44   $43.45   $43.40  
  Purchase #6 $162.91   6.579%   $173.6278   $173.63   $173.65   $173.60  
  Purchase #7 $230.35   6.747%   $245.8917   $245.89   $245.90   $245.90  
  7 purchase totals = $698.76       $742.2024   $742.21   $742.25   $742.20