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 $86.40   11.452%   $96.2945   $96.29   $96.30   $96.30  
  Purchase #2 $227.45   7.524%   $244.5633   $244.56   $244.55   $244.60  
  Purchase #3 $114.89   6.593%   $122.4647   $122.46   $122.45   $122.50  
  Purchase #4 $163.83   10.129%   $180.4243   $180.42   $180.40   $180.40  
  Purchase #5 $184.76   7.217%   $198.0941   $198.09   $198.10   $198.10  
  Purchase #6 $203.44   6.287%   $216.2303   $216.23   $216.25   $216.20  
  Purchase #7 $41.54   4.843%   $43.5518   $43.55   $43.55   $43.60  
  7 purchase totals = $1,022.31       $1,101.6230   $1,101.60   $1,101.60   $1,101.70