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 $22.53   6.799%   $24.0618   $24.06   $24.05   $24.10  
  Purchase #2 $111.34   12.677%   $125.4546   $125.45   $125.45   $125.50  
  Purchase #3 $28.45   4.258%   $29.6614   $29.66   $29.65   $29.70  
  Purchase #4 $183.49   10.285%   $202.3619   $202.36   $202.35   $202.40  
  Purchase #5 $182.61   6.756%   $194.9471   $194.95   $194.95   $194.90  
  Purchase #6 $60.90   3.490%   $63.0254   $63.03   $63.05   $63.00  
  Purchase #7 $64.47   9.581%   $70.6469   $70.65   $70.65   $70.60  
  7 purchase totals = $653.79       $710.1591   $710.16   $710.15   $710.20