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 $239.37   11.739%   $267.4696   $267.47   $267.45   $267.50  
  Purchase #2 $45.83   5.749%   $48.4648   $48.46   $48.45   $48.50  
  Purchase #3 $57.88   3.122%   $59.687   $59.69   $59.70   $59.70  
  Purchase #4 $46.74   5.254%   $49.1957   $49.20   $49.20   $49.20  
  Purchase #5 $202.70   6.422%   $215.7174   $215.72   $215.70   $215.70  
  Purchase #6 $208.30   11.570%   $232.4003   $232.40   $232.40   $232.40  
  Purchase #7 $45.92   3.525%   $47.5387   $47.54   $47.55   $47.50  
  7 purchase totals = $846.74       $920.4735   $920.48   $920.45   $920.50