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 $238.48   9.700%   $261.6126   $261.61   $261.60   $261.60  
  Purchase #2 $177.33   10.507%   $195.9621   $195.96   $195.95   $196.00  
  Purchase #3 $24.57   9.126%   $26.8123   $26.81   $26.80   $26.80  
  Purchase #4 $192.33   4.767%   $201.4984   $201.50   $201.50   $201.50  
  Purchase #5 $19.32   13.413%   $21.9114   $21.91   $21.90   $21.90  
  Purchase #6 $195.84   5.761%   $207.1223   $207.12   $207.10   $207.10  
  Purchase #7 $45.79   13.684%   $52.0559   $52.06   $52.05   $52.10  
  7 purchase totals = $893.66       $966.9750   $966.97   $966.90   $967.00