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 $54.54   12.354%   $61.2779   $61.28   $61.30   $61.30  
  Purchase #2 $162.50   7.322%   $174.3983   $174.40   $174.40   $174.40  
  Purchase #3 $224.37   10.722%   $248.427   $248.43   $248.45   $248.40  
  Purchase #4 $76.69   13.797%   $87.2709   $87.27   $87.25   $87.30  
  Purchase #5 $89.64   7.345%   $96.2241   $96.22   $96.20   $96.20  
  Purchase #6 $49.45   10.552%   $54.668   $54.67   $54.65   $54.70  
  Purchase #7 $17.88   12.132%   $20.0492   $20.05   $20.05   $20.00  
  7 purchase totals = $675.07       $742.3154   $742.32   $742.30   $742.30