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 $60.29   9.613%   $66.0857   $66.09   $66.10   $66.10  
  Purchase #2 $176.45   3.604%   $182.8093   $182.81   $182.80   $182.80  
  Purchase #3 $19.70   7.362%   $21.1503   $21.15   $21.15   $21.20  
  Purchase #4 $178.70   8.424%   $193.7537   $193.75   $193.75   $193.80  
  Purchase #5 $62.92   9.756%   $69.0585   $69.06   $69.05   $69.10  
  Purchase #6 $250.90   10.437%   $277.0864   $277.09   $277.10   $277.10  
  Purchase #7 $138.67   8.169%   $149.998   $150.00   $150.00   $150.00  
  7 purchase totals = $887.63       $959.9419   $959.95   $959.95   $960.10