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 $52.48   13.685%   $59.6619   $59.66   $59.65   $59.70  
  Purchase #2 $102.44   8.120%   $110.7581   $110.76   $110.75   $110.80  
  Purchase #3 $94.27   4.229%   $98.2567   $98.26   $98.25   $98.30  
  Purchase #4 $94.66   3.450%   $97.9258   $97.93   $97.95   $97.90  
  Purchase #5 $173.37   10.769%   $192.0402   $192.04   $192.05   $192.00  
  Purchase #6 $200.25   6.796%   $213.859   $213.86   $213.85   $213.90  
  Purchase #7 $214.52   3.705%   $222.468   $222.47   $222.45   $222.50  
  7 purchase totals = $931.99       $994.9697   $994.98   $994.95   $995.10