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 $194.28   13.167%   $219.8608   $219.86   $219.85   $219.90  
  Purchase #2 $82.56   8.399%   $89.4942   $89.49   $89.50   $89.50  
  Purchase #3 $180.64   8.476%   $195.951   $195.95   $195.95   $196.00  
  Purchase #4 $146.27   11.662%   $163.328   $163.33   $163.35   $163.30  
  Purchase #5 $119.65   12.631%   $134.763   $134.76   $134.75   $134.80  
  Purchase #6 $128.41   5.593%   $135.592   $135.59   $135.60   $135.60  
  Purchase #7 $175.82   5.225%   $185.0066   $185.01   $185.00   $185.00  
  7 purchase totals = $1,027.63       $1,123.9956   $1,123.99   $1,124.00   $1,124.10