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 $211.84   13.832%   $241.1417   $241.14   $241.15   $241.10  
  Purchase #2 $93.76   8.423%   $101.6574   $101.66   $101.65   $101.70  
  Purchase #3 $69.70   5.186%   $73.3146   $73.31   $73.30   $73.30  
  Purchase #4 $59.68   8.288%   $64.6263   $64.63   $64.65   $64.60  
  Purchase #5 $201.80   11.781%   $225.5741   $225.57   $225.55   $225.60  
  Purchase #6 $50.32   12.378%   $56.5486   $56.55   $56.55   $56.50  
  Purchase #7 $232.84   8.627%   $252.9271   $252.93   $252.95   $252.90  
  7 purchase totals = $919.94       $1,015.7898   $1,015.79   $1,015.80   $1,015.70