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 $72.82   5.363%   $76.7253   $76.73   $76.75   $76.70  
  Purchase #2 $56.51   9.406%   $61.8253   $61.83   $61.85   $61.80  
  Purchase #3 $201.97   6.244%   $214.581   $214.58   $214.60   $214.60  
  Purchase #4 $213.71   12.794%   $241.0521   $241.05   $241.05   $241.10  
  Purchase #5 $219.93   10.791%   $243.6626   $243.66   $243.65   $243.70  
  Purchase #6 $187.57   6.647%   $200.0378   $200.04   $200.05   $200.00  
  Purchase #7 $46.53   4.597%   $48.669   $48.67   $48.65   $48.70  
  7 purchase totals = $999.04       $1,086.5531   $1,086.56   $1,086.60   $1,086.60