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 $196.52   10.170%   $216.5061   $216.51   $216.50   $216.50  
  Purchase #2 $230.65   9.539%   $252.6517   $252.65   $252.65   $252.70  
  Purchase #3 $26.42   8.245%   $28.5983   $28.60   $28.60   $28.60  
  Purchase #4 $32.67   3.786%   $33.9069   $33.91   $33.90   $33.90  
  Purchase #5 $92.51   10.693%   $102.4021   $102.40   $102.40   $102.40  
  Purchase #6 $153.80   3.860%   $159.7367   $159.74   $159.75   $159.70  
  Purchase #7 $169.48   9.762%   $186.0246   $186.02   $186.00   $186.00  
  7 purchase totals = $902.05       $979.8264   $979.83   $979.80   $979.80