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 $52.97   9.728%   $58.1229   $58.12   $58.10   $58.10  
  Purchase #2 $208.81   11.613%   $233.0591   $233.06   $233.05   $233.10  
  Purchase #3 $205.70   11.510%   $229.3761   $229.38   $229.40   $229.40  
  Purchase #4 $89.72   7.867%   $96.7783   $96.78   $96.80   $96.80  
  Purchase #5 $108.32   5.805%   $114.608   $114.61   $114.60   $114.60  
  Purchase #6 $200.79   8.599%   $218.0559   $218.06   $218.05   $218.10  
  Purchase #7 $59.46   6.280%   $63.1941   $63.19   $63.20   $63.20  
  7 purchase totals = $925.77       $1,013.1944   $1,013.20   $1,013.20   $1,013.30