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 $175.67   6.167%   $186.5036   $186.50   $186.50   $186.50  
  Purchase #2 $204.96   3.265%   $211.6519   $211.65   $211.65   $211.70  
  Purchase #3 $51.53   12.780%   $58.1155   $58.12   $58.10   $58.10  
  Purchase #4 $241.59   11.221%   $268.6988   $268.70   $268.70   $268.70  
  Purchase #5 $144.56   6.602%   $154.1039   $154.10   $154.10   $154.10  
  Purchase #6 $68.50   13.693%   $77.8797   $77.88   $77.90   $77.90  
  Purchase #7 $26.61   12.753%   $30.0036   $30.00   $30.00   $30.00  
  7 purchase totals = $913.42       $986.9570   $986.95   $986.95   $987.00