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 $180.71   3.248%   $186.5795   $186.58   $186.60   $186.60  
  Purchase #2 $203.96   12.142%   $228.7248   $228.72   $228.70   $228.70  
  Purchase #3 $236.84   12.636%   $266.7671   $266.77   $266.75   $266.80  
  Purchase #4 $120.26   13.623%   $136.643   $136.64   $136.65   $136.60  
  Purchase #5 $133.40   11.591%   $148.8624   $148.86   $148.85   $148.90  
  Purchase #6 $208.30   9.313%   $227.699   $227.70   $227.70   $227.70  
  Purchase #7 $40.70   4.160%   $42.3931   $42.39   $42.40   $42.40  
  7 purchase totals = $1,124.17       $1,237.6689   $1,237.66   $1,237.65   $1,237.70