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 $81.76   13.833%   $93.0699   $93.07   $93.05   $93.10  
  Purchase #2 $172.79   7.770%   $186.2158   $186.22   $186.20   $186.20  
  Purchase #3 $195.29   9.405%   $213.657   $213.66   $213.65   $213.70  
  Purchase #4 $158.45   4.693%   $165.8861   $165.89   $165.90   $165.90  
  Purchase #5 $216.82   5.311%   $228.3353   $228.34   $228.35   $228.30  
  Purchase #6 $155.28   7.667%   $167.1853   $167.19   $167.20   $167.20  
  Purchase #7 $136.59   8.532%   $148.2439   $148.24   $148.25   $148.20  
  7 purchase totals = $1,116.98       $1,202.5933   $1,202.61   $1,202.60   $1,202.60