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 $172.77   6.761%   $184.451   $184.45   $184.45   $184.50  
  Purchase #2 $59.78   5.392%   $63.0033   $63.00   $63.00   $63.00  
  Purchase #3 $100.62   7.216%   $107.8807   $107.88   $107.90   $107.90  
  Purchase #4 $233.78   3.688%   $242.4018   $242.40   $242.40   $242.40  
  Purchase #5 $57.65   11.711%   $64.4014   $64.40   $64.40   $64.40  
  Purchase #6 $76.40   11.244%   $84.9904   $84.99   $85.00   $85.00  
  Purchase #7 $72.57   12.865%   $81.9061   $81.91   $81.90   $81.90  
  7 purchase totals = $773.57       $829.0347   $829.03   $829.05   $829.10