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 $69.30   10.572%   $76.6264   $76.63   $76.65   $76.60  
  Purchase #2 $134.90   12.582%   $151.8731   $151.87   $151.85   $151.90  
  Purchase #3 $53.59   6.797%   $57.2325   $57.23   $57.25   $57.20  
  Purchase #4 $81.95   8.830%   $89.1862   $89.19   $89.20   $89.20  
  Purchase #5 $208.84   11.394%   $232.6352   $232.64   $232.65   $232.60  
  Purchase #6 $121.68   13.685%   $138.3319   $138.33   $138.35   $138.30  
  Purchase #7 $239.76   8.623%   $260.4345   $260.43   $260.45   $260.40  
  7 purchase totals = $910.02       $1,006.3198   $1,006.32   $1,006.40   $1,006.20