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 $31.63   11.310%   $35.2074   $35.21   $35.20   $35.20  
  Purchase #2 $162.57   7.362%   $174.5384   $174.54   $174.55   $174.50  
  Purchase #3 $107.81   11.719%   $120.4443   $120.44   $120.45   $120.40  
  Purchase #4 $180.29   6.491%   $191.9926   $191.99   $192.00   $192.00  
  Purchase #5 $56.87   5.823%   $60.1815   $60.18   $60.20   $60.20  
  Purchase #6 $240.91   5.449%   $254.0372   $254.04   $254.05   $254.00  
  Purchase #7 $213.79   6.250%   $227.1519   $227.15   $227.15   $227.20  
  7 purchase totals = $993.87       $1,063.5533   $1,063.55   $1,063.60   $1,063.50