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 $23.99   7.169%   $25.7098   $25.71   $25.70   $25.70  
  Purchase #2 $199.86   4.411%   $208.6758   $208.68   $208.70   $208.70  
  Purchase #3 $190.89   5.782%   $201.9273   $201.93   $201.95   $201.90  
  Purchase #4 $216.88   7.570%   $233.2978   $233.30   $233.30   $233.30  
  Purchase #5 $61.28   11.618%   $68.3995   $68.40   $68.40   $68.40  
  Purchase #6 $118.37   7.566%   $127.3259   $127.33   $127.35   $127.30  
  Purchase #7 $64.26   11.639%   $71.7392   $71.74   $71.75   $71.70  
  7 purchase totals = $875.53       $937.0753   $937.09   $937.15   $937.00