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 $146.48   5.637%   $154.7371   $154.74   $154.75   $154.70  
  Purchase #2 $24.70   8.801%   $26.8738   $26.87   $26.85   $26.90  
  Purchase #3 $78.74   7.872%   $84.9384   $84.94   $84.95   $84.90  
  Purchase #4 $217.91   7.445%   $234.1334   $234.13   $234.15   $234.10  
  Purchase #5 $177.27   8.799%   $192.868   $192.87   $192.85   $192.90  
  Purchase #6 $170.84   3.594%   $176.98   $176.98   $177.00   $177.00  
  Purchase #7 $56.42   7.163%   $60.4614   $60.46   $60.45   $60.50  
  7 purchase totals = $872.36       $930.9921   $930.99   $931.00   $931.00