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 $141.54   13.704%   $160.9366   $160.94   $160.95   $160.90  
  Purchase #2 $168.91   13.430%   $191.5946   $191.59   $191.60   $191.60  
  Purchase #3 $228.77   12.791%   $258.032   $258.03   $258.05   $258.00  
  Purchase #4 $67.32   8.755%   $73.2139   $73.21   $73.20   $73.20  
  Purchase #5 $31.46   6.372%   $33.4646   $33.46   $33.45   $33.50  
  Purchase #6 $17.83   10.477%   $19.698   $19.70   $19.70   $19.70  
  Purchase #7 $111.70   4.104%   $116.2842   $116.28   $116.30   $116.30  
  7 purchase totals = $767.53       $853.2239   $853.21   $853.25   $853.20