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 $159.91   10.448%   $176.6174   $176.62   $176.60   $176.60  
  Purchase #2 $228.52   9.400%   $250.0009   $250.00   $250.00   $250.00  
  Purchase #3 $118.93   10.445%   $131.3522   $131.35   $131.35   $131.40  
  Purchase #4 $20.90   5.687%   $22.0886   $22.09   $22.10   $22.10  
  Purchase #5 $211.26   13.413%   $239.5963   $239.60   $239.60   $239.60  
  Purchase #6 $168.78   9.641%   $185.0521   $185.05   $185.05   $185.10  
  Purchase #7 $237.90   10.367%   $262.5631   $262.56   $262.55   $262.60  
  7 purchase totals = $1,146.20       $1,267.2706   $1,267.27   $1,267.25   $1,267.40