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 $225.73   13.404%   $255.9868   $255.99   $256.00   $256.00  
  Purchase #2 $54.48   12.556%   $61.3205   $61.32   $61.30   $61.30  
  Purchase #3 $233.77   3.132%   $241.0917   $241.09   $241.10   $241.10  
  Purchase #4 $56.72   3.578%   $58.7494   $58.75   $58.75   $58.70  
  Purchase #5 $165.48   11.251%   $184.0982   $184.10   $184.10   $184.10  
  Purchase #6 $160.90   12.640%   $181.2378   $181.24   $181.25   $181.20  
  Purchase #7 $214.73   5.451%   $226.4349   $226.43   $226.45   $226.40  
  7 purchase totals = $1,111.81       $1,208.9193   $1,208.92   $1,208.95   $1,208.80