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 $235.79   3.282%   $243.5286   $243.53   $243.55   $243.50  
  Purchase #2 $152.76   4.645%   $159.8557   $159.86   $159.85   $159.90  
  Purchase #3 $183.52   13.269%   $207.8713   $207.87   $207.85   $207.90  
  Purchase #4 $186.43   5.284%   $196.281   $196.28   $196.30   $196.30  
  Purchase #5 $39.61   6.547%   $42.2033   $42.20   $42.20   $42.20  
  Purchase #6 $166.87   5.716%   $176.4083   $176.41   $176.40   $176.40  
  Purchase #7 $223.41   6.450%   $237.8199   $237.82   $237.80   $237.80  
  7 purchase totals = $1,188.39       $1,263.9681   $1,263.97   $1,263.95   $1,264.00