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 $48.84   5.668%   $51.6083   $51.61   $51.60   $51.60  
  Purchase #2 $184.58   11.663%   $206.1076   $206.11   $206.10   $206.10  
  Purchase #3 $105.83   4.316%   $110.3976   $110.40   $110.40   $110.40  
  Purchase #4 $77.68   8.761%   $84.4855   $84.49   $84.50   $84.50  
  Purchase #5 $55.30   13.694%   $62.8728   $62.87   $62.85   $62.90  
  Purchase #6 $155.67   12.353%   $174.8999   $174.90   $174.90   $174.90  
  Purchase #7 $151.41   8.346%   $164.0467   $164.05   $164.05   $164.00  
  7 purchase totals = $779.31       $854.4184   $854.43   $854.40   $854.40