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 $186.92   11.731%   $208.8476   $208.85   $208.85   $208.80  
  Purchase #2 $45.99   13.548%   $52.2207   $52.22   $52.20   $52.20  
  Purchase #3 $179.48   6.406%   $190.9775   $190.98   $191.00   $191.00  
  Purchase #4 $250.86   12.664%   $282.6289   $282.63   $282.65   $282.60  
  Purchase #5 $96.27   11.667%   $107.5018   $107.50   $107.50   $107.50  
  Purchase #6 $148.58   9.573%   $162.8036   $162.80   $162.80   $162.80  
  Purchase #7 $202.93   5.858%   $214.8176   $214.82   $214.80   $214.80  
  7 purchase totals = $1,111.03       $1,219.7977   $1,219.80   $1,219.80   $1,219.70