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 $166.67   11.599%   $186.0021   $186.00   $186.00   $186.00  
  Purchase #2 $119.38   10.336%   $131.7191   $131.72   $131.70   $131.70  
  Purchase #3 $191.72   10.838%   $212.4986   $212.50   $212.50   $212.50  
  Purchase #4 $207.86   8.679%   $225.9002   $225.90   $225.90   $225.90  
  Purchase #5 $36.63   6.655%   $39.0677   $39.07   $39.05   $39.10  
  Purchase #6 $24.25   7.399%   $26.0443   $26.04   $26.05   $26.00  
  Purchase #7 $187.55   11.848%   $209.7709   $209.77   $209.75   $209.80  
  7 purchase totals = $934.06       $1,031.0029   $1,031.00   $1,030.95   $1,031.00