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 $87.81   9.574%   $96.2169   $96.22   $96.20   $96.20  
  Purchase #2 $203.45   3.174%   $209.9075   $209.91   $209.90   $209.90  
  Purchase #3 $174.79   7.137%   $187.2648   $187.26   $187.25   $187.30  
  Purchase #4 $93.79   12.154%   $105.1892   $105.19   $105.20   $105.20  
  Purchase #5 $93.26   5.467%   $98.3585   $98.36   $98.35   $98.40  
  Purchase #6 $236.55   5.543%   $249.662   $249.66   $249.65   $249.70  
  Purchase #7 $87.99   6.740%   $93.9205   $93.92   $93.90   $93.90  
  7 purchase totals = $977.64       $1,040.5194   $1,040.52   $1,040.45   $1,040.60