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 $112.95   5.347%   $118.9894   $118.99   $119.00   $119.00  
  Purchase #2 $166.25   9.651%   $182.2948   $182.29   $182.30   $182.30  
  Purchase #3 $189.94   12.855%   $214.3568   $214.36   $214.35   $214.40  
  Purchase #4 $53.26   5.195%   $56.0269   $56.03   $56.05   $56.00  
  Purchase #5 $120.29   3.296%   $124.2548   $124.25   $124.25   $124.30  
  Purchase #6 $72.85   4.214%   $75.9199   $75.92   $75.90   $75.90  
  Purchase #7 $203.95   8.255%   $220.7861   $220.79   $220.80   $220.80  
  7 purchase totals = $919.49       $992.6287   $992.63   $992.65   $992.70