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 $239.60   9.314%   $261.9163   $261.92   $261.90   $261.90  
  Purchase #2 $127.33   3.168%   $131.3638   $131.36   $131.35   $131.40  
  Purchase #3 $19.75   4.425%   $20.6239   $20.62   $20.60   $20.60  
  Purchase #4 $93.83   3.508%   $97.1216   $97.12   $97.10   $97.10  
  Purchase #5 $65.69   3.675%   $68.1041   $68.10   $68.10   $68.10  
  Purchase #6 $235.57   10.377%   $260.0151   $260.02   $260.00   $260.00  
  Purchase #7 $36.31   4.573%   $37.9705   $37.97   $37.95   $38.00  
  7 purchase totals = $818.08       $877.1153   $877.11   $877.00   $877.10