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 $176.39   11.453%   $196.5919   $196.59   $196.60   $196.60  
  Purchase #2 $214.27   5.783%   $226.6612   $226.66   $226.65   $226.70  
  Purchase #3 $207.62   4.832%   $217.6522   $217.65   $217.65   $217.70  
  Purchase #4 $232.44   3.278%   $240.0594   $240.06   $240.05   $240.10  
  Purchase #5 $104.78   6.114%   $111.1862   $111.19   $111.20   $111.20  
  Purchase #6 $54.74   7.268%   $58.7185   $58.72   $58.70   $58.70  
  Purchase #7 $196.76   8.433%   $213.3528   $213.35   $213.35   $213.40  
  7 purchase totals = $1,187.00       $1,264.2222   $1,264.22   $1,264.20   $1,264.40