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 $43.68   7.336%   $46.8844   $46.88   $46.90   $46.90  
  Purchase #2 $31.44   9.321%   $34.3705   $34.37   $34.35   $34.40  
  Purchase #3 $241.25   13.807%   $274.5594   $274.56   $274.55   $274.60  
  Purchase #4 $207.27   8.108%   $224.0755   $224.08   $224.10   $224.10  
  Purchase #5 $100.76   5.477%   $106.2786   $106.28   $106.30   $106.30  
  Purchase #6 $14.58   13.285%   $16.517   $16.52   $16.50   $16.50  
  Purchase #7 $236.58   5.164%   $248.797   $248.80   $248.80   $248.80  
  7 purchase totals = $875.56       $951.4824   $951.49   $951.50   $951.60