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 $182.67   10.368%   $201.6092   $201.61   $201.60   $201.60  
  Purchase #2 $138.25   4.812%   $144.9026   $144.90   $144.90   $144.90  
  Purchase #3 $96.53   5.846%   $102.1731   $102.17   $102.15   $102.20  
  Purchase #4 $24.42   12.833%   $27.5538   $27.55   $27.55   $27.60  
  Purchase #5 $227.85   7.559%   $245.0732   $245.07   $245.05   $245.10  
  Purchase #6 $98.68   5.792%   $104.3955   $104.40   $104.40   $104.40  
  Purchase #7 $8.37   13.628%   $9.5107   $9.51   $9.50   $9.50  
  7 purchase totals = $776.77       $835.2181   $835.21   $835.15   $835.30