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 $248.55   11.622%   $277.4365   $277.44   $277.45   $277.40  
  Purchase #2 $179.29   10.588%   $198.2732   $198.27   $198.25   $198.30  
  Purchase #3 $219.44   3.260%   $226.5937   $226.59   $226.60   $226.60  
  Purchase #4 $62.56   10.142%   $68.9048   $68.90   $68.90   $68.90  
  Purchase #5 $26.76   10.355%   $29.531   $29.53   $29.55   $29.50  
  Purchase #6 $132.56   11.663%   $148.0205   $148.02   $148.00   $148.00  
  Purchase #7 $78.41   5.495%   $82.7186   $82.72   $82.70   $82.70  
  7 purchase totals = $947.57       $1,031.4783   $1,031.47   $1,031.45   $1,031.40