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 $176.95   12.409%   $198.9077   $198.91   $198.90   $198.90  
  Purchase #2 $216.87   3.274%   $223.9703   $223.97   $223.95   $224.00  
  Purchase #3 $54.49   7.587%   $58.6242   $58.62   $58.60   $58.60  
  Purchase #4 $63.70   5.773%   $67.3774   $67.38   $67.40   $67.40  
  Purchase #5 $9.33   5.424%   $9.8361   $9.84   $9.85   $9.80  
  Purchase #6 $51.86   9.216%   $56.6394   $56.64   $56.65   $56.60  
  Purchase #7 $33.98   5.152%   $35.7306   $35.73   $35.75   $35.70  
  7 purchase totals = $607.18       $651.0857   $651.09   $651.10   $651.00