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 $207.33   13.524%   $235.3693   $235.37   $235.35   $235.40  
  Purchase #2 $122.37   9.506%   $134.0025   $134.00   $134.00   $134.00  
  Purchase #3 $51.95   10.741%   $57.5299   $57.53   $57.55   $57.50  
  Purchase #4 $60.53   11.429%   $67.448   $67.45   $67.45   $67.40  
  Purchase #5 $187.40   4.658%   $196.1291   $196.13   $196.15   $196.10  
  Purchase #6 $6.29   4.542%   $6.5757   $6.58   $6.60   $6.60  
  Purchase #7 $228.27   3.849%   $237.0561   $237.06   $237.05   $237.10  
  7 purchase totals = $864.14       $934.1106   $934.12   $934.15   $934.10