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 $176.89   11.658%   $197.5118   $197.51   $197.50   $197.50  
  Purchase #2 $55.96   3.220%   $57.7619   $57.76   $57.75   $57.80  
  Purchase #3 $39.80   8.135%   $43.0377   $43.04   $43.05   $43.00  
  Purchase #4 $173.39   3.183%   $178.909   $178.91   $178.90   $178.90  
  Purchase #5 $213.59   12.590%   $240.481   $240.48   $240.50   $240.50  
  Purchase #6 $85.77   9.125%   $93.5965   $93.60   $93.60   $93.60  
  Purchase #7 $35.54   6.257%   $37.7637   $37.76   $37.75   $37.80  
  7 purchase totals = $780.94       $849.0616   $849.06   $849.05   $849.10