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 $237.77   11.597%   $265.3442   $265.34   $265.35   $265.30  
  Purchase #2 $99.92   12.813%   $112.7227   $112.72   $112.70   $112.70  
  Purchase #3 $201.25   11.593%   $224.5809   $224.58   $224.60   $224.60  
  Purchase #4 $63.57   8.239%   $68.8075   $68.81   $68.80   $68.80  
  Purchase #5 $166.87   13.318%   $189.0937   $189.09   $189.10   $189.10  
  Purchase #6 $151.86   13.838%   $172.8744   $172.87   $172.85   $172.90  
  Purchase #7 $95.43   3.722%   $98.9819   $98.98   $99.00   $99.00  
  7 purchase totals = $1,016.67       $1,132.4053   $1,132.39   $1,132.40   $1,132.40