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 $161.77   10.558%   $178.8497   $178.85   $178.85   $178.80  
  Purchase #2 $229.27   10.157%   $252.557   $252.56   $252.55   $252.60  
  Purchase #3 $159.82   12.546%   $179.871   $179.87   $179.85   $179.90  
  Purchase #4 $40.40   5.464%   $42.6075   $42.61   $42.60   $42.60  
  Purchase #5 $245.93   4.225%   $256.3205   $256.32   $256.30   $256.30  
  Purchase #6 $56.74   9.747%   $62.2704   $62.27   $62.25   $62.30  
  Purchase #7 $23.77   9.617%   $26.056   $26.06   $26.05   $26.10  
  7 purchase totals = $917.70       $998.5321   $998.54   $998.45   $998.60