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 $53.50   10.654%   $59.1999   $59.20   $59.20   $59.20  
  Purchase #2 $180.53   6.380%   $192.0478   $192.05   $192.05   $192.00  
  Purchase #3 $218.42   12.289%   $245.2616   $245.26   $245.25   $245.30  
  Purchase #4 $49.98   9.620%   $54.7881   $54.79   $54.80   $54.80  
  Purchase #5 $219.99   13.766%   $250.2738   $250.27   $250.25   $250.30  
  Purchase #6 $242.38   8.135%   $262.0976   $262.10   $262.10   $262.10  
  Purchase #7 $200.45   10.250%   $220.9961   $221.00   $221.00   $221.00  
  7 purchase totals = $1,165.25       $1,284.6649   $1,284.67   $1,284.65   $1,284.70