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 $201.42   11.819%   $225.2258   $225.23   $225.25   $225.20  
  Purchase #2 $184.30   12.749%   $207.7964   $207.80   $207.80   $207.80  
  Purchase #3 $95.59   3.391%   $98.8315   $98.83   $98.85   $98.80  
  Purchase #4 $56.91   6.623%   $60.6791   $60.68   $60.70   $60.70  
  Purchase #5 $120.81   7.485%   $129.8526   $129.85   $129.85   $129.90  
  Purchase #6 $130.61   4.183%   $136.0734   $136.07   $136.05   $136.10  
  Purchase #7 $5.53   8.767%   $6.0148   $6.01   $6.00   $6.00  
  7 purchase totals = $795.17       $864.4736   $864.47   $864.50   $864.50