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 $61.78   13.636%   $70.2043   $70.20   $70.20   $70.20  
  Purchase #2 $248.36   11.394%   $276.6581   $276.66   $276.65   $276.70  
  Purchase #3 $23.40   5.224%   $24.6224   $24.62   $24.60   $24.60  
  Purchase #4 $128.45   11.774%   $143.5737   $143.57   $143.55   $143.60  
  Purchase #5 $28.67   6.732%   $30.6001   $30.60   $30.60   $30.60  
  Purchase #6 $61.53   5.512%   $64.9215   $64.92   $64.90   $64.90  
  Purchase #7 $231.25   11.826%   $258.5976   $258.60   $258.60   $258.60  
  7 purchase totals = $783.44       $869.1777   $869.17   $869.10   $869.20