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 $95.92   9.233%   $104.7763   $104.78   $104.80   $104.80  
  Purchase #2 $23.44   6.602%   $24.9875   $24.99   $25.00   $25.00  
  Purchase #3 $50.78   13.705%   $57.7394   $57.74   $57.75   $57.70  
  Purchase #4 $136.91   3.806%   $142.1208   $142.12   $142.10   $142.10  
  Purchase #5 $118.99   7.731%   $128.1891   $128.19   $128.20   $128.20  
  Purchase #6 $126.50   5.310%   $133.2172   $133.22   $133.20   $133.20  
  Purchase #7 $55.68   4.208%   $58.023   $58.02   $58.00   $58.00  
  7 purchase totals = $608.22       $649.0533   $649.06   $649.05   $649.00