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 $60.65   8.501%   $65.8059   $65.81   $65.80   $65.80  
  Purchase #2 $157.84   3.846%   $163.9105   $163.91   $163.90   $163.90  
  Purchase #3 $150.97   3.357%   $156.0381   $156.04   $156.05   $156.00  
  Purchase #4 $181.56   7.819%   $195.7562   $195.76   $195.75   $195.80  
  Purchase #5 $49.29   5.117%   $51.8122   $51.81   $51.80   $51.80  
  Purchase #6 $82.68   13.637%   $93.9551   $93.96   $93.95   $94.00  
  Purchase #7 $214.54   6.545%   $228.5816   $228.58   $228.60   $228.60  
  7 purchase totals = $897.53       $955.8596   $955.87   $955.85   $955.90