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 $119.58   11.456%   $133.2791   $133.28   $133.30   $133.30  
  Purchase #2 $177.66   13.533%   $201.7027   $201.70   $201.70   $201.70  
  Purchase #3 $118.93   13.870%   $135.4256   $135.43   $135.45   $135.40  
  Purchase #4 $186.43   6.240%   $198.0632   $198.06   $198.05   $198.10  
  Purchase #5 $101.90   3.492%   $105.4583   $105.46   $105.45   $105.50  
  Purchase #6 $159.82   11.586%   $178.3367   $178.34   $178.35   $178.30  
  Purchase #7 $33.69   10.444%   $37.2086   $37.21   $37.20   $37.20  
  7 purchase totals = $898.01       $989.4742   $989.48   $989.50   $989.50