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 $218.91   6.298%   $232.697   $232.70   $232.70   $232.70  
  Purchase #2 $124.62   10.624%   $137.8596   $137.86   $137.85   $137.90  
  Purchase #3 $211.75   5.806%   $224.0442   $224.04   $224.05   $224.00  
  Purchase #4 $202.26   7.162%   $216.7459   $216.75   $216.75   $216.70  
  Purchase #5 $115.83   13.558%   $131.5342   $131.53   $131.55   $131.50  
  Purchase #6 $83.90   10.508%   $92.7162   $92.72   $92.70   $92.70  
  Purchase #7 $247.86   4.616%   $259.3012   $259.30   $259.30   $259.30  
  7 purchase totals = $1,205.13       $1,294.8983   $1,294.90   $1,294.90   $1,294.80