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 $68.55   13.277%   $77.6514   $77.65   $77.65   $77.70  
  Purchase #2 $114.91   6.652%   $122.5538   $122.55   $122.55   $122.60  
  Purchase #3 $244.93   4.410%   $255.7314   $255.73   $255.75   $255.70  
  Purchase #4 $26.44   4.479%   $27.6242   $27.62   $27.60   $27.60  
  Purchase #5 $244.46   4.586%   $255.6709   $255.67   $255.65   $255.70  
  Purchase #6 $163.91   5.539%   $172.989   $172.99   $173.00   $173.00  
  Purchase #7 $88.59   13.212%   $100.2945   $100.29   $100.30   $100.30  
  7 purchase totals = $951.79       $1,012.5152   $1,012.50   $1,012.50   $1,012.60