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 $171.84   13.505%   $195.047   $195.05   $195.05   $195.00  
  Purchase #2 $41.68   7.385%   $44.7581   $44.76   $44.75   $44.80  
  Purchase #3 $207.40   9.234%   $226.5513   $226.55   $226.55   $226.60  
  Purchase #4 $209.41   10.807%   $232.0409   $232.04   $232.05   $232.00  
  Purchase #5 $114.96   10.380%   $126.8928   $126.89   $126.90   $126.90  
  Purchase #6 $192.56   7.406%   $206.821   $206.82   $206.80   $206.80  
  Purchase #7 $18.32   5.429%   $19.3146   $19.31   $19.30   $19.30  
  7 purchase totals = $956.17       $1,051.4257   $1,051.42   $1,051.40   $1,051.40