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 $49.58   7.380%   $53.239   $53.24   $53.25   $53.20  
  Purchase #2 $122.34   3.363%   $126.4543   $126.45   $126.45   $126.50  
  Purchase #3 $23.33   7.641%   $25.1126   $25.11   $25.10   $25.10  
  Purchase #4 $199.36   13.210%   $225.6955   $225.70   $225.70   $225.70  
  Purchase #5 $139.53   13.782%   $158.76   $158.76   $158.75   $158.80  
  Purchase #6 $166.25   6.447%   $176.9681   $176.97   $176.95   $177.00  
  Purchase #7 $128.57   5.144%   $135.1836   $135.18   $135.20   $135.20  
  7 purchase totals = $828.96       $901.4131   $901.41   $901.40   $901.50