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 $62.26   13.792%   $70.8469   $70.85   $70.85   $70.80  
  Purchase #2 $211.65   13.173%   $239.5307   $239.53   $239.55   $239.50  
  Purchase #3 $89.53   5.842%   $94.7603   $94.76   $94.75   $94.80  
  Purchase #4 $22.50   8.451%   $24.4015   $24.40   $24.40   $24.40  
  Purchase #5 $35.32   12.268%   $39.6531   $39.65   $39.65   $39.70  
  Purchase #6 $155.58   12.414%   $174.8937   $174.89   $174.90   $174.90  
  Purchase #7 $62.32   7.606%   $67.0601   $67.06   $67.05   $67.10  
  7 purchase totals = $639.16       $711.1463   $711.14   $711.15   $711.20