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 $145.50   7.331%   $156.1666   $156.17   $156.15   $156.20  
  Purchase #2 $25.75   3.277%   $26.5938   $26.59   $26.60   $26.60  
  Purchase #3 $196.69   9.158%   $214.7029   $214.70   $214.70   $214.70  
  Purchase #4 $117.28   11.104%   $130.3028   $130.30   $130.30   $130.30  
  Purchase #5 $106.70   13.433%   $121.033   $121.03   $121.05   $121.00  
  Purchase #6 $215.30   5.771%   $227.725   $227.73   $227.75   $227.70  
  Purchase #7 $71.60   9.663%   $78.5187   $78.52   $78.50   $78.50  
  7 purchase totals = $878.82       $955.0428   $955.04   $955.05   $955.00