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 $207.86   10.160%   $228.9786   $228.98   $229.00   $229.00  
  Purchase #2 $122.84   9.658%   $134.7039   $134.70   $134.70   $134.70  
  Purchase #3 $57.99   10.767%   $64.2338   $64.23   $64.25   $64.20  
  Purchase #4 $112.84   10.140%   $124.282   $124.28   $124.30   $124.30  
  Purchase #5 $75.49   8.207%   $81.6855   $81.69   $81.70   $81.70  
  Purchase #6 $152.35   8.699%   $165.6029   $165.60   $165.60   $165.60  
  Purchase #7 $232.65   12.522%   $261.7824   $261.78   $261.80   $261.80  
  7 purchase totals = $962.02       $1,061.2691   $1,061.26   $1,061.35   $1,061.30