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 $162.91   13.704%   $185.2352   $185.24   $185.25   $185.20  
  Purchase #2 $55.28   8.133%   $59.7759   $59.78   $59.80   $59.80  
  Purchase #3 $114.61   12.655%   $129.1139   $129.11   $129.10   $129.10  
  Purchase #4 $124.79   9.600%   $136.7698   $136.77   $136.75   $136.80  
  Purchase #5 $53.95   13.569%   $61.2705   $61.27   $61.25   $61.30  
  Purchase #6 $127.59   6.536%   $135.9293   $135.93   $135.95   $135.90  
  Purchase #7 $67.31   6.324%   $71.5667   $71.57   $71.55   $71.60  
  7 purchase totals = $706.44       $779.6613   $779.67   $779.65   $779.70