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 $244.74   10.144%   $269.5664   $269.57   $269.55   $269.60  
  Purchase #2 $179.91   3.830%   $186.8006   $186.80   $186.80   $186.80  
  Purchase #3 $112.84   13.867%   $128.4875   $128.49   $128.50   $128.50  
  Purchase #4 $29.39   7.587%   $31.6198   $31.62   $31.60   $31.60  
  Purchase #5 $115.69   7.663%   $124.5553   $124.56   $124.55   $124.60  
  Purchase #6 $193.37   7.681%   $208.2227   $208.22   $208.20   $208.20  
  Purchase #7 $202.66   11.806%   $226.586   $226.59   $226.60   $226.60  
  7 purchase totals = $1,078.60       $1,175.8383   $1,175.85   $1,175.80   $1,175.90