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 $49.61   8.396%   $53.7753   $53.78   $53.80   $53.80  
  Purchase #2 $79.96   13.621%   $90.8514   $90.85   $90.85   $90.90  
  Purchase #3 $171.88   7.449%   $184.6833   $184.68   $184.70   $184.70  
  Purchase #4 $25.27   5.233%   $26.5924   $26.59   $26.60   $26.60  
  Purchase #5 $168.83   4.745%   $176.841   $176.84   $176.85   $176.80  
  Purchase #6 $207.91   13.217%   $235.3895   $235.39   $235.40   $235.40  
  Purchase #7 $40.60   11.607%   $45.3124   $45.31   $45.30   $45.30  
  7 purchase totals = $744.06       $813.4453   $813.44   $813.50   $813.50