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 $137.77   7.437%   $148.016   $148.02   $148.00   $148.00  
  Purchase #2 $53.26   5.414%   $56.1435   $56.14   $56.15   $56.10  
  Purchase #3 $163.64   3.812%   $169.878   $169.88   $169.90   $169.90  
  Purchase #4 $236.37   13.616%   $268.5541   $268.55   $268.55   $268.60  
  Purchase #5 $219.41   10.607%   $242.6828   $242.68   $242.70   $242.70  
  Purchase #6 $207.75   8.505%   $225.4191   $225.42   $225.40   $225.40  
  Purchase #7 $44.42   4.195%   $46.2834   $46.28   $46.30   $46.30  
  7 purchase totals = $1,062.62       $1,156.9769   $1,156.97   $1,157.00   $1,157.00