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 $93.44   13.238%   $105.8096   $105.81   $105.80   $105.80  
  Purchase #2 $26.79   8.673%   $29.1135   $29.11   $29.10   $29.10  
  Purchase #3 $151.88   7.114%   $162.6847   $162.68   $162.70   $162.70  
  Purchase #4 $59.86   4.844%   $62.7596   $62.76   $62.75   $62.80  
  Purchase #5 $237.49   11.287%   $264.2955   $264.30   $264.30   $264.30  
  Purchase #6 $116.55   6.359%   $123.9614   $123.96   $123.95   $124.00  
  Purchase #7 $53.66   4.301%   $55.9679   $55.97   $55.95   $56.00  
  7 purchase totals = $739.67       $804.5922   $804.59   $804.55   $804.70