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 $45.81   10.364%   $50.5577   $50.56   $50.55   $50.60  
  Purchase #2 $247.25   5.565%   $261.0095   $261.01   $261.00   $261.00  
  Purchase #3 $194.70   5.111%   $204.6511   $204.65   $204.65   $204.70  
  Purchase #4 $16.70   3.420%   $17.2711   $17.27   $17.25   $17.30  
  Purchase #5 $132.49   10.708%   $146.677   $146.68   $146.70   $146.70  
  Purchase #6 $173.81   3.261%   $179.4779   $179.48   $179.50   $179.50  
  Purchase #7 $165.46   13.524%   $187.8368   $187.84   $187.85   $187.80  
  7 purchase totals = $976.22       $1,047.4811   $1,047.49   $1,047.50   $1,047.60