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 $85.48   12.867%   $96.4787   $96.48   $96.50   $96.50  
  Purchase #2 $181.90   5.444%   $191.8026   $191.80   $191.80   $191.80  
  Purchase #3 $189.84   11.384%   $211.4514   $211.45   $211.45   $211.50  
  Purchase #4 $242.69   7.367%   $260.569   $260.57   $260.55   $260.60  
  Purchase #5 $162.86   6.719%   $173.8026   $173.80   $173.80   $173.80  
  Purchase #6 $103.83   11.196%   $115.4548   $115.45   $115.45   $115.50  
  Purchase #7 $28.65   5.466%   $30.216   $30.22   $30.20   $30.20  
  7 purchase totals = $995.25       $1,079.7751   $1,079.77   $1,079.75   $1,079.90