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 $239.56   9.316%   $261.8774   $261.88   $261.90   $261.90  
  Purchase #2 $69.46   7.741%   $74.8369   $74.84   $74.85   $74.80  
  Purchase #3 $124.53   8.671%   $135.328   $135.33   $135.35   $135.30  
  Purchase #4 $147.47   4.482%   $154.0796   $154.08   $154.10   $154.10  
  Purchase #5 $44.59   9.520%   $48.835   $48.84   $48.85   $48.80  
  Purchase #6 $76.87   5.164%   $80.8396   $80.84   $80.85   $80.80  
  Purchase #7 $243.54   9.507%   $266.6933   $266.69   $266.70   $266.70  
  7 purchase totals = $946.02       $1,022.4898   $1,022.50   $1,022.60   $1,022.40