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 $192.86   8.717%   $209.6716   $209.67   $209.65   $209.70  
  Purchase #2 $103.78   12.652%   $116.9102   $116.91   $116.90   $116.90  
  Purchase #3 $17.91   8.783%   $19.483   $19.48   $19.50   $19.50  
  Purchase #4 $153.27   12.124%   $171.8525   $171.85   $171.85   $171.90  
  Purchase #5 $81.76   11.570%   $91.2196   $91.22   $91.20   $91.20  
  Purchase #6 $198.74   4.650%   $207.9814   $207.98   $208.00   $208.00  
  Purchase #7 $27.84   12.599%   $31.3476   $31.35   $31.35   $31.30  
  7 purchase totals = $776.16       $848.4659   $848.46   $848.45   $848.50