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 $211.49   11.234%   $235.2488   $235.25   $235.25   $235.20  
  Purchase #2 $28.53   4.768%   $29.8903   $29.89   $29.90   $29.90  
  Purchase #3 $77.48   4.138%   $80.6861   $80.69   $80.70   $80.70  
  Purchase #4 $195.27   8.195%   $211.2724   $211.27   $211.25   $211.30  
  Purchase #5 $127.62   10.458%   $140.9665   $140.97   $140.95   $141.00  
  Purchase #6 $62.25   9.282%   $68.028   $68.03   $68.05   $68.00  
  Purchase #7 $9.62   9.560%   $10.5397   $10.54   $10.55   $10.50  
  7 purchase totals = $712.26       $776.6318   $776.64   $776.65   $776.60