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 $146.32   5.432%   $154.2681   $154.27   $154.25   $154.30  
  Purchase #2 $174.79   5.818%   $184.9593   $184.96   $184.95   $185.00  
  Purchase #3 $161.76   6.354%   $172.0382   $172.04   $172.05   $172.00  
  Purchase #4 $45.99   8.629%   $49.9585   $49.96   $49.95   $50.00  
  Purchase #5 $94.94   11.289%   $105.6578   $105.66   $105.65   $105.70  
  Purchase #6 $115.35   8.296%   $124.9194   $124.92   $124.90   $124.90  
  Purchase #7 $247.98   12.553%   $279.1089   $279.11   $279.10   $279.10  
  7 purchase totals = $987.13       $1,070.9102   $1,070.92   $1,070.85   $1,071.00