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 $20.56   10.822%   $22.785   $22.79   $22.80   $22.80  
  Purchase #2 $112.67   10.661%   $124.6817   $124.68   $124.70   $124.70  
  Purchase #3 $15.47   9.400%   $16.9242   $16.92   $16.90   $16.90  
  Purchase #4 $44.29   4.433%   $46.2534   $46.25   $46.25   $46.30  
  Purchase #5 $186.44   3.469%   $192.9076   $192.91   $192.90   $192.90  
  Purchase #6 $120.35   7.214%   $129.032   $129.03   $129.05   $129.00  
  Purchase #7 $43.38   12.729%   $48.9018   $48.90   $48.90   $48.90  
  7 purchase totals = $543.16       $581.4857   $581.48   $581.50   $581.50