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 $232.94   12.433%   $261.9014   $261.90   $261.90   $261.90  
  Purchase #2 $180.82   3.169%   $186.5502   $186.55   $186.55   $186.60  
  Purchase #3 $179.85   7.583%   $193.488   $193.49   $193.50   $193.50  
  Purchase #4 $81.28   9.640%   $89.1154   $89.12   $89.10   $89.10  
  Purchase #5 $168.57   11.747%   $188.3719   $188.37   $188.35   $188.40  
  Purchase #6 $206.88   12.423%   $232.5807   $232.58   $232.60   $232.60  
  Purchase #7 $141.79   5.643%   $149.7912   $149.79   $149.80   $149.80  
  7 purchase totals = $1,192.13       $1,301.7988   $1,301.80   $1,301.80   $1,301.90