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 $58.86   9.470%   $64.434   $64.43   $64.45   $64.40  
  Purchase #2 $106.26   9.431%   $116.2814   $116.28   $116.30   $116.30  
  Purchase #3 $243.42   9.671%   $266.9611   $266.96   $266.95   $267.00  
  Purchase #4 $215.81   6.757%   $230.3923   $230.39   $230.40   $230.40  
  Purchase #5 $78.27   9.206%   $85.4755   $85.48   $85.50   $85.50  
  Purchase #6 $233.57   3.528%   $241.8103   $241.81   $241.80   $241.80  
  Purchase #7 $17.90   6.215%   $19.0125   $19.01   $19.00   $19.00  
  7 purchase totals = $954.09       $1,024.3671   $1,024.36   $1,024.40   $1,024.40