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 $216.90   13.353%   $245.8627   $245.86   $245.85   $245.90  
  Purchase #2 $208.56   9.642%   $228.6694   $228.67   $228.65   $228.70  
  Purchase #3 $162.57   8.157%   $175.8308   $175.83   $175.85   $175.80  
  Purchase #4 $249.27   7.820%   $268.7629   $268.76   $268.75   $268.80  
  Purchase #5 $36.26   10.166%   $39.9462   $39.95   $39.95   $39.90  
  Purchase #6 $219.83   3.849%   $228.2913   $228.29   $228.30   $228.30  
  Purchase #7 $10.53   9.553%   $11.5359   $11.54   $11.55   $11.50  
  7 purchase totals = $1,103.92       $1,198.8992   $1,198.90   $1,198.90   $1,198.90