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 $153.58   13.712%   $174.6389   $174.64   $174.65   $174.60  
  Purchase #2 $134.89   12.481%   $151.7256   $151.73   $151.75   $151.70  
  Purchase #3 $241.69   3.810%   $250.8984   $250.90   $250.90   $250.90  
  Purchase #4 $143.36   6.263%   $152.3386   $152.34   $152.35   $152.30  
  Purchase #5 $57.41   10.220%   $63.2773   $63.28   $63.30   $63.30  
  Purchase #6 $227.60   3.501%   $235.5683   $235.57   $235.55   $235.60  
  Purchase #7 $5.40   4.233%   $5.6286   $5.63   $5.65   $5.60  
  7 purchase totals = $963.93       $1,034.0757   $1,034.09   $1,034.15   $1,034.00