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 $67.28   8.768%   $73.1791   $73.18   $73.20   $73.20  
  Purchase #2 $231.70   13.712%   $263.4707   $263.47   $263.45   $263.50  
  Purchase #3 $213.86   13.749%   $243.2636   $243.26   $243.25   $243.30  
  Purchase #4 $16.88   6.234%   $17.9323   $17.93   $17.95   $17.90  
  Purchase #5 $202.94   5.586%   $214.2762   $214.28   $214.30   $214.30  
  Purchase #6 $165.96   7.141%   $177.8112   $177.81   $177.80   $177.80  
  Purchase #7 $247.70   7.716%   $266.8125   $266.81   $266.80   $266.80  
  7 purchase totals = $1,146.32       $1,256.7456   $1,256.74   $1,256.75   $1,256.80