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 $42.48   12.434%   $47.762   $47.76   $47.75   $47.80  
  Purchase #2 $114.32   7.558%   $122.9603   $122.96   $122.95   $123.00  
  Purchase #3 $159.41   6.601%   $169.9327   $169.93   $169.95   $169.90  
  Purchase #4 $121.62   8.186%   $131.5758   $131.58   $131.60   $131.60  
  Purchase #5 $24.74   3.174%   $25.5252   $25.53   $25.55   $25.50  
  Purchase #6 $114.95   8.825%   $125.0943   $125.09   $125.10   $125.10  
  Purchase #7 $206.37   6.621%   $220.0338   $220.03   $220.05   $220.00  
  7 purchase totals = $783.89       $842.8841   $842.88   $842.95   $842.90