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 $190.80   6.162%   $202.5571   $202.56   $202.55   $202.60  
  Purchase #2 $228.97   6.325%   $243.4524   $243.45   $243.45   $243.50  
  Purchase #3 $82.58   13.759%   $93.9422   $93.94   $93.95   $93.90  
  Purchase #4 $63.77   12.662%   $71.8446   $71.84   $71.85   $71.80  
  Purchase #5 $103.80   10.289%   $114.48   $114.48   $114.50   $114.50  
  Purchase #6 $165.50   5.640%   $174.8342   $174.83   $174.85   $174.80  
  Purchase #7 $53.69   11.849%   $60.0517   $60.05   $60.05   $60.10  
  7 purchase totals = $889.11       $961.1622   $961.15   $961.20   $961.20