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 $153.53   6.621%   $163.6952   $163.70   $163.70   $163.70  
  Purchase #2 $62.55   6.791%   $66.7978   $66.80   $66.80   $66.80  
  Purchase #3 $117.93   5.296%   $124.1756   $124.18   $124.20   $124.20  
  Purchase #4 $220.94   10.188%   $243.4494   $243.45   $243.45   $243.40  
  Purchase #5 $49.34   12.518%   $55.5164   $55.52   $55.50   $55.50  
  Purchase #6 $248.63   8.501%   $269.766   $269.77   $269.75   $269.80  
  Purchase #7 $87.60   12.555%   $98.5982   $98.60   $98.60   $98.60  
  7 purchase totals = $940.52       $1,021.9986   $1,022.02   $1,022.00   $1,022.00