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 $64.75   13.718%   $73.6324   $73.63   $73.65   $73.60  
  Purchase #2 $154.27   7.555%   $165.9251   $165.93   $165.95   $165.90  
  Purchase #3 $193.40   4.129%   $201.3855   $201.39   $201.40   $201.40  
  Purchase #4 $48.66   9.633%   $53.3474   $53.35   $53.35   $53.30  
  Purchase #5 $186.35   13.436%   $211.388   $211.39   $211.40   $211.40  
  Purchase #6 $32.41   4.156%   $33.757   $33.76   $33.75   $33.80  
  Purchase #7 $57.45   3.640%   $59.5412   $59.54   $59.55   $59.50  
  7 purchase totals = $737.29       $798.9766   $798.99   $799.05   $798.90