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 $84.47   9.284%   $92.3122   $92.31   $92.30   $92.30  
  Purchase #2 $132.59   10.794%   $146.9018   $146.90   $146.90   $146.90  
  Purchase #3 $53.25   10.362%   $58.7678   $58.77   $58.75   $58.80  
  Purchase #4 $176.42   4.622%   $184.5741   $184.57   $184.55   $184.60  
  Purchase #5 $193.37   5.354%   $203.723   $203.72   $203.70   $203.70  
  Purchase #6 $214.74   11.760%   $239.9934   $239.99   $240.00   $240.00  
  Purchase #7 $49.78   8.565%   $54.0437   $54.04   $54.05   $54.00  
  7 purchase totals = $904.62       $980.3160   $980.30   $980.25   $980.30