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 $234.26   13.130%   $265.0183   $265.02   $265.00   $265.00  
  Purchase #2 $214.39   12.670%   $241.5532   $241.55   $241.55   $241.60  
  Purchase #3 $56.68   3.710%   $58.7828   $58.78   $58.80   $58.80  
  Purchase #4 $241.33   13.329%   $273.4969   $273.50   $273.50   $273.50  
  Purchase #5 $233.64   7.303%   $250.7027   $250.70   $250.70   $250.70  
  Purchase #6 $120.66   8.670%   $131.1212   $131.12   $131.10   $131.10  
  Purchase #7 $87.66   8.380%   $95.0059   $95.01   $95.00   $95.00  
  7 purchase totals = $1,188.62       $1,315.6810   $1,315.68   $1,315.65   $1,315.70