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 $43.26   13.764%   $49.2143   $49.21   $49.20   $49.20  
  Purchase #2 $226.42   3.630%   $234.639   $234.64   $234.65   $234.60  
  Purchase #3 $248.67   6.357%   $264.478   $264.48   $264.50   $264.50  
  Purchase #4 $243.38   6.277%   $258.657   $258.66   $258.65   $258.70  
  Purchase #5 $192.49   5.631%   $203.3291   $203.33   $203.35   $203.30  
  Purchase #6 $167.54   6.530%   $178.4804   $178.48   $178.50   $178.50  
  Purchase #7 $47.57   10.231%   $52.4369   $52.44   $52.45   $52.40  
  7 purchase totals = $1,169.33       $1,241.2347   $1,241.24   $1,241.30   $1,241.20