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 $146.53   12.848%   $165.3562   $165.36   $165.35   $165.40  
  Purchase #2 $201.72   9.393%   $220.6676   $220.67   $220.65   $220.70  
  Purchase #3 $124.77   13.871%   $142.0768   $142.08   $142.10   $142.10  
  Purchase #4 $65.92   9.202%   $71.986   $71.99   $72.00   $72.00  
  Purchase #5 $55.73   9.525%   $61.0383   $61.04   $61.05   $61.00  
  Purchase #6 $133.93   10.172%   $147.5534   $147.55   $147.55   $147.60  
  Purchase #7 $63.37   7.568%   $68.1658   $68.17   $68.15   $68.20  
  7 purchase totals = $791.97       $876.8441   $876.86   $876.85   $877.00