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 $247.84   8.144%   $268.0241   $268.02   $268.00   $268.00  
  Purchase #2 $127.51   6.524%   $135.8288   $135.83   $135.85   $135.80  
  Purchase #3 $66.65   9.293%   $72.8438   $72.84   $72.85   $72.80  
  Purchase #4 $31.97   6.512%   $34.0519   $34.05   $34.05   $34.10  
  Purchase #5 $248.42   7.787%   $267.7645   $267.76   $267.75   $267.80  
  Purchase #6 $229.60   12.302%   $257.8454   $257.85   $257.85   $257.80  
  Purchase #7 $162.42   5.714%   $171.7007   $171.70   $171.70   $171.70  
  7 purchase totals = $1,114.41       $1,208.0592   $1,208.05   $1,208.05   $1,208.00