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 $163.53   13.656%   $185.8617   $185.86   $185.85   $185.90  
  Purchase #2 $212.30   10.691%   $234.997   $235.00   $235.00   $235.00  
  Purchase #3 $49.94   6.156%   $53.0143   $53.01   $53.00   $53.00  
  Purchase #4 $143.67   13.301%   $162.7795   $162.78   $162.80   $162.80  
  Purchase #5 $151.47   9.233%   $165.4552   $165.46   $165.45   $165.50  
  Purchase #6 $60.32   6.213%   $64.0677   $64.07   $64.05   $64.10  
  Purchase #7 $194.25   7.532%   $208.8809   $208.88   $208.90   $208.90  
  7 purchase totals = $975.48       $1,075.0563   $1,075.06   $1,075.05   $1,075.20