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 $153.76   4.722%   $161.0205   $161.02   $161.00   $161.00  
  Purchase #2 $73.79   5.536%   $77.875   $77.88   $77.90   $77.90  
  Purchase #3 $46.67   13.481%   $52.9616   $52.96   $52.95   $53.00  
  Purchase #4 $139.96   5.870%   $148.1757   $148.18   $148.20   $148.20  
  Purchase #5 $105.29   6.454%   $112.0854   $112.09   $112.10   $112.10  
  Purchase #6 $247.31   12.382%   $277.9319   $277.93   $277.95   $277.90  
  Purchase #7 $177.57   7.394%   $190.6995   $190.70   $190.70   $190.70  
  7 purchase totals = $944.35       $1,020.7496   $1,020.76   $1,020.80   $1,020.80