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 $243.96   7.734%   $262.8279   $262.83   $262.85   $262.80  
  Purchase #2 $56.51   9.621%   $61.9468   $61.95   $61.95   $61.90  
  Purchase #3 $38.71   7.656%   $41.6736   $41.67   $41.65   $41.70  
  Purchase #4 $72.33   13.217%   $81.8899   $81.89   $81.90   $81.90  
  Purchase #5 $112.94   8.734%   $122.8042   $122.80   $122.80   $122.80  
  Purchase #6 $241.75   8.461%   $262.2045   $262.20   $262.20   $262.20  
  Purchase #7 $45.60   6.271%   $48.4596   $48.46   $48.45   $48.50  
  7 purchase totals = $811.80       $881.8065   $881.80   $881.80   $881.80