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 $69.40   9.616%   $76.0735   $76.07   $76.05   $76.10  
  Purchase #2 $197.42   6.867%   $210.9768   $210.98   $211.00   $211.00  
  Purchase #3 $101.45   3.371%   $104.8699   $104.87   $104.85   $104.90  
  Purchase #4 $110.99   3.715%   $115.1133   $115.11   $115.10   $115.10  
  Purchase #5 $140.35   9.365%   $153.4938   $153.49   $153.50   $153.50  
  Purchase #6 $61.45   5.231%   $64.6644   $64.66   $64.65   $64.70  
  Purchase #7 $51.38   4.829%   $53.8611   $53.86   $53.85   $53.90  
  7 purchase totals = $732.44       $779.0528   $779.04   $779.00   $779.20