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 $219.36   11.530%   $244.6522   $244.65   $244.65   $244.70  
  Purchase #2 $41.54   9.774%   $45.6001   $45.60   $45.60   $45.60  
  Purchase #3 $218.43   6.125%   $231.8088   $231.81   $231.80   $231.80  
  Purchase #4 $156.77   9.868%   $172.2401   $172.24   $172.25   $172.20  
  Purchase #5 $77.57   4.502%   $81.0622   $81.06   $81.05   $81.10  
  Purchase #6 $35.45   5.384%   $37.3586   $37.36   $37.35   $37.40  
  Purchase #7 $156.68   3.267%   $161.7987   $161.80   $161.80   $161.80  
  7 purchase totals = $905.80       $974.5207   $974.52   $974.50   $974.60