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 $119.89   5.206%   $126.1315   $126.13   $126.15   $126.10  
  Purchase #2 $163.26   10.526%   $180.4447   $180.44   $180.45   $180.40  
  Purchase #3 $151.59   7.705%   $163.27   $163.27   $163.25   $163.30  
  Purchase #4 $109.64   11.115%   $121.8265   $121.83   $121.85   $121.80  
  Purchase #5 $211.61   5.323%   $222.874   $222.87   $222.85   $222.90  
  Purchase #6 $129.78   12.149%   $145.547   $145.55   $145.55   $145.50  
  Purchase #7 $18.46   9.424%   $20.1997   $20.20   $20.20   $20.20  
  7 purchase totals = $904.23       $980.2934   $980.29   $980.30   $980.20