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 $95.99   11.611%   $107.1354   $107.14   $107.15   $107.10  
  Purchase #2 $172.41   12.262%   $193.5509   $193.55   $193.55   $193.60  
  Purchase #3 $238.74   13.661%   $271.3543   $271.35   $271.35   $271.40  
  Purchase #4 $57.60   8.782%   $62.6584   $62.66   $62.65   $62.70  
  Purchase #5 $70.76   4.201%   $73.7326   $73.73   $73.75   $73.70  
  Purchase #6 $174.97   9.331%   $191.2965   $191.30   $191.30   $191.30  
  Purchase #7 $108.59   9.567%   $118.9788   $118.98   $119.00   $119.00  
  7 purchase totals = $919.06       $1,018.7069   $1,018.71   $1,018.75   $1,018.80