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 $80.83   5.399%   $85.194   $85.19   $85.20   $85.20  
  Purchase #2 $70.64   3.423%   $73.058   $73.06   $73.05   $73.10  
  Purchase #3 $147.86   4.786%   $154.9366   $154.94   $154.95   $154.90  
  Purchase #4 $250.31   7.758%   $269.729   $269.73   $269.75   $269.70  
  Purchase #5 $66.81   7.178%   $71.6056   $71.61   $71.60   $71.60  
  Purchase #6 $174.92   9.313%   $191.2103   $191.21   $191.20   $191.20  
  Purchase #7 $68.97   12.154%   $77.3526   $77.35   $77.35   $77.40  
  7 purchase totals = $860.34       $923.0861   $923.09   $923.10   $923.10