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 $59.34   6.419%   $63.149   $63.15   $63.15   $63.10  
  Purchase #2 $72.54   7.753%   $78.164   $78.16   $78.15   $78.20  
  Purchase #3 $47.54   11.439%   $52.9781   $52.98   $53.00   $53.00  
  Purchase #4 $204.70   10.639%   $226.478   $226.48   $226.50   $226.50  
  Purchase #5 $161.67   7.138%   $173.21   $173.21   $173.20   $173.20  
  Purchase #6 $219.79   13.110%   $248.6045   $248.60   $248.60   $248.60  
  Purchase #7 $134.36   7.111%   $143.9143   $143.91   $143.90   $143.90  
  7 purchase totals = $899.94       $986.4979   $986.49   $986.50   $986.50