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 $243.91   4.814%   $255.6518   $255.65   $255.65   $255.70  
  Purchase #2 $250.26   6.578%   $266.7221   $266.72   $266.70   $266.70  
  Purchase #3 $11.29   12.379%   $12.6876   $12.69   $12.70   $12.70  
  Purchase #4 $179.33   10.519%   $198.1937   $198.19   $198.20   $198.20  
  Purchase #5 $33.76   5.308%   $35.552   $35.55   $35.55   $35.60  
  Purchase #6 $43.52   12.581%   $48.9953   $49.00   $49.00   $49.00  
  Purchase #7 $188.71   10.225%   $208.0056   $208.01   $208.00   $208.00  
  7 purchase totals = $950.78       $1,025.8081   $1,025.81   $1,025.80   $1,025.90