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 $113.39   9.149%   $123.7641   $123.76   $123.75   $123.80  
  Purchase #2 $243.41   5.770%   $257.4548   $257.45   $257.45   $257.50  
  Purchase #3 $108.56   4.272%   $113.1977   $113.20   $113.20   $113.20  
  Purchase #4 $120.90   4.293%   $126.0902   $126.09   $126.10   $126.10  
  Purchase #5 $111.78   5.306%   $117.711   $117.71   $117.70   $117.70  
  Purchase #6 $213.60   6.478%   $227.437   $227.44   $227.45   $227.40  
  Purchase #7 $53.83   5.363%   $56.7169   $56.72   $56.70   $56.70  
  7 purchase totals = $965.47       $1,022.3717   $1,022.37   $1,022.35   $1,022.40