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 $167.66   13.348%   $190.0393   $190.04   $190.05   $190.00  
  Purchase #2 $76.34   7.721%   $82.2342   $82.23   $82.25   $82.20  
  Purchase #3 $98.55   7.576%   $106.0161   $106.02   $106.00   $106.00  
  Purchase #4 $225.78   10.831%   $250.2342   $250.23   $250.25   $250.20  
  Purchase #5 $216.25   3.772%   $224.407   $224.41   $224.40   $224.40  
  Purchase #6 $48.50   4.670%   $50.765   $50.77   $50.75   $50.80  
  Purchase #7 $120.79   7.683%   $130.0703   $130.07   $130.05   $130.10  
  7 purchase totals = $953.87       $1,033.7661   $1,033.77   $1,033.75   $1,033.70