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 $165.83   12.759%   $186.9882   $186.99   $187.00   $187.00  
  Purchase #2 $25.28   6.543%   $26.9341   $26.93   $26.95   $26.90  
  Purchase #3 $159.41   10.382%   $175.9599   $175.96   $175.95   $176.00  
  Purchase #4 $188.68   9.664%   $206.914   $206.91   $206.90   $206.90  
  Purchase #5 $199.68   6.547%   $212.753   $212.75   $212.75   $212.80  
  Purchase #6 $128.38   7.654%   $138.2062   $138.21   $138.20   $138.20  
  Purchase #7 $228.57   12.856%   $257.955   $257.96   $257.95   $258.00  
  7 purchase totals = $1,095.83       $1,205.7104   $1,205.71   $1,205.70   $1,205.80