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 $97.91   8.857%   $106.5819   $106.58   $106.60   $106.60  
  Purchase #2 $205.54   7.372%   $220.6924   $220.69   $220.70   $220.70  
  Purchase #3 $193.79   10.363%   $213.8725   $213.87   $213.85   $213.90  
  Purchase #4 $44.45   12.469%   $49.9925   $49.99   $50.00   $50.00  
  Purchase #5 $163.36   6.381%   $173.784   $173.78   $173.80   $173.80  
  Purchase #6 $109.58   3.640%   $113.5687   $113.57   $113.55   $113.60  
  Purchase #7 $168.95   5.592%   $178.3977   $178.40   $178.40   $178.40  
  7 purchase totals = $983.58       $1,056.8897   $1,056.88   $1,056.90   $1,057.00