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 $38.72   11.816%   $43.2952   $43.30   $43.30   $43.30  
  Purchase #2 $89.92   4.462%   $93.9322   $93.93   $93.95   $93.90  
  Purchase #3 $111.54   13.452%   $126.5444   $126.54   $126.55   $126.50  
  Purchase #4 $79.36   11.219%   $88.2634   $88.26   $88.25   $88.30  
  Purchase #5 $49.90   13.214%   $56.4938   $56.49   $56.50   $56.50  
  Purchase #6 $245.68   7.789%   $264.816   $264.82   $264.80   $264.80  
  Purchase #7 $152.45   7.241%   $163.4889   $163.49   $163.50   $163.50  
  7 purchase totals = $767.57       $836.8339   $836.83   $836.85   $836.80