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 $133.61   13.164%   $151.1984   $151.20   $151.20   $151.20  
  Purchase #2 $109.88   8.314%   $119.0154   $119.02   $119.00   $119.00  
  Purchase #3 $43.77   4.372%   $45.6836   $45.68   $45.70   $45.70  
  Purchase #4 $149.99   13.381%   $170.0602   $170.06   $170.05   $170.10  
  Purchase #5 $167.39   11.524%   $186.68   $186.68   $186.70   $186.70  
  Purchase #6 $8.36   10.773%   $9.2606   $9.26   $9.25   $9.30  
  Purchase #7 $94.49   11.623%   $105.4726   $105.47   $105.45   $105.50  
  7 purchase totals = $707.49       $787.3708   $787.37   $787.35   $787.50