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 $212.76   4.353%   $222.0214   $222.02   $222.00   $222.00  
  Purchase #2 $245.76   9.429%   $268.9327   $268.93   $268.95   $268.90  
  Purchase #3 $226.73   10.702%   $250.9946   $250.99   $251.00   $251.00  
  Purchase #4 $94.92   6.874%   $101.4448   $101.44   $101.45   $101.40  
  Purchase #5 $232.83   7.683%   $250.7183   $250.72   $250.70   $250.70  
  Purchase #6 $187.81   3.370%   $194.1392   $194.14   $194.15   $194.10  
  Purchase #7 $203.54   6.424%   $216.6154   $216.62   $216.60   $216.60  
  7 purchase totals = $1,404.35       $1,504.8664   $1,504.86   $1,504.85   $1,504.70