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 $24.53   3.234%   $25.3233   $25.32   $25.30   $25.30  
  Purchase #2 $219.44   6.159%   $232.9553   $232.96   $232.95   $233.00  
  Purchase #3 $76.26   7.116%   $81.6867   $81.69   $81.70   $81.70  
  Purchase #4 $94.46   11.625%   $105.441   $105.44   $105.45   $105.40  
  Purchase #5 $207.36   12.750%   $233.7984   $233.80   $233.80   $233.80  
  Purchase #6 $211.88   6.289%   $225.2051   $225.21   $225.20   $225.20  
  Purchase #7 $163.34   6.275%   $173.5896   $173.59   $173.60   $173.60  
  7 purchase totals = $997.27       $1,077.9994   $1,078.01   $1,078.00   $1,078.00