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 $35.70   5.654%   $37.7185   $37.72   $37.70   $37.70  
  Purchase #2 $206.45   8.492%   $223.9817   $223.98   $224.00   $224.00  
  Purchase #3 $35.26   5.689%   $37.2659   $37.27   $37.25   $37.30  
  Purchase #4 $168.41   7.652%   $181.2967   $181.30   $181.30   $181.30  
  Purchase #5 $27.51   3.400%   $28.4453   $28.45   $28.45   $28.40  
  Purchase #6 $235.99   5.120%   $248.0727   $248.07   $248.05   $248.10  
  Purchase #7 $186.50   3.573%   $193.1636   $193.16   $193.15   $193.20  
  7 purchase totals = $895.82       $949.9444   $949.95   $949.90   $950.00