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 $63.41   8.313%   $68.6813   $68.68   $68.70   $68.70  
  Purchase #2 $148.87   9.359%   $162.8027   $162.80   $162.80   $162.80  
  Purchase #3 $241.57   12.379%   $271.474   $271.47   $271.45   $271.50  
  Purchase #4 $22.96   4.705%   $24.0403   $24.04   $24.05   $24.00  
  Purchase #5 $49.63   7.663%   $53.4331   $53.43   $53.45   $53.40  
  Purchase #6 $120.58   12.533%   $135.6923   $135.69   $135.70   $135.70  
  Purchase #7 $37.54   8.259%   $40.6404   $40.64   $40.65   $40.60  
  7 purchase totals = $684.56       $756.7641   $756.75   $756.80   $756.70