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 $32.37   4.826%   $33.9322   $33.93   $33.95   $33.90  
  Purchase #2 $179.71   7.230%   $192.703   $192.70   $192.70   $192.70  
  Purchase #3 $68.57   12.447%   $77.1049   $77.10   $77.10   $77.10  
  Purchase #4 $51.39   6.835%   $54.9025   $54.90   $54.90   $54.90  
  Purchase #5 $247.74   8.844%   $269.6501   $269.65   $269.65   $269.70  
  Purchase #6 $173.71   8.119%   $187.8135   $187.81   $187.80   $187.80  
  Purchase #7 $77.84   8.637%   $84.563   $84.56   $84.55   $84.60  
  7 purchase totals = $831.33       $900.6692   $900.65   $900.65   $900.70