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 $87.78   9.136%   $95.7996   $95.80   $95.80   $95.80  
  Purchase #2 $104.57   10.587%   $115.6408   $115.64   $115.65   $115.60  
  Purchase #3 $104.58   10.110%   $115.153   $115.15   $115.15   $115.20  
  Purchase #4 $239.49   13.873%   $272.7144   $272.71   $272.70   $272.70  
  Purchase #5 $186.63   4.769%   $195.5304   $195.53   $195.55   $195.50  
  Purchase #6 $210.40   3.186%   $217.1033   $217.10   $217.10   $217.10  
  Purchase #7 $70.80   11.635%   $79.0376   $79.04   $79.05   $79.00  
  7 purchase totals = $1,004.25       $1,090.9791   $1,090.97   $1,091.00   $1,090.90