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 $22.96   8.349%   $24.8769   $24.88   $24.90   $24.90  
  Purchase #2 $222.81   5.571%   $235.2227   $235.22   $235.20   $235.20  
  Purchase #3 $101.33   13.768%   $115.2811   $115.28   $115.30   $115.30  
  Purchase #4 $80.52   10.106%   $88.6574   $88.66   $88.65   $88.70  
  Purchase #5 $54.72   5.391%   $57.67   $57.67   $57.65   $57.70  
  Purchase #6 $225.26   12.824%   $254.1473   $254.15   $254.15   $254.10  
  Purchase #7 $43.47   7.692%   $46.8137   $46.81   $46.80   $46.80  
  7 purchase totals = $751.07       $822.6691   $822.67   $822.65   $822.70