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 $115.88   9.260%   $126.6105   $126.61   $126.60   $126.60  
  Purchase #2 $166.85   5.629%   $176.242   $176.24   $176.25   $176.20  
  Purchase #3 $124.82   11.215%   $138.8186   $138.82   $138.80   $138.80  
  Purchase #4 $24.70   6.308%   $26.2581   $26.26   $26.25   $26.30  
  Purchase #5 $202.51   6.277%   $215.2216   $215.22   $215.20   $215.20  
  Purchase #6 $132.75   13.839%   $151.1213   $151.12   $151.10   $151.10  
  Purchase #7 $12.40   13.349%   $14.0553   $14.06   $14.05   $14.10  
  7 purchase totals = $779.91       $848.3274   $848.33   $848.25   $848.30