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 $243.51   8.698%   $264.6905   $264.69   $264.70   $264.70  
  Purchase #2 $10.28   8.598%   $11.1639   $11.16   $11.15   $11.20  
  Purchase #3 $49.41   7.161%   $52.9483   $52.95   $52.95   $52.90  
  Purchase #4 $237.47   11.839%   $265.5841   $265.58   $265.60   $265.60  
  Purchase #5 $203.97   10.277%   $224.932   $224.93   $224.95   $224.90  
  Purchase #6 $52.45   11.446%   $58.4534   $58.45   $58.45   $58.50  
  Purchase #7 $53.84   10.160%   $59.3101   $59.31   $59.30   $59.30  
  7 purchase totals = $850.93       $937.0823   $937.07   $937.10   $937.10