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 $66.91   13.543%   $75.9716   $75.97   $75.95   $76.00  
  Purchase #2 $199.45   10.585%   $220.5618   $220.56   $220.55   $220.60  
  Purchase #3 $121.51   10.847%   $134.6902   $134.69   $134.70   $134.70  
  Purchase #4 $11.86   5.251%   $12.4828   $12.48   $12.50   $12.50  
  Purchase #5 $245.62   3.369%   $253.8949   $253.89   $253.90   $253.90  
  Purchase #6 $124.98   4.734%   $130.8966   $130.90   $130.90   $130.90  
  Purchase #7 $26.75   8.486%   $29.02   $29.02   $29.00   $29.00  
  7 purchase totals = $797.08       $857.5179   $857.51   $857.50   $857.60