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 $56.98   8.710%   $61.943   $61.94   $61.95   $61.90  
  Purchase #2 $34.67   8.244%   $37.5282   $37.53   $37.55   $37.50  
  Purchase #3 $169.38   4.797%   $177.5052   $177.51   $177.50   $177.50  
  Purchase #4 $54.80   6.770%   $58.51   $58.51   $58.50   $58.50  
  Purchase #5 $180.81   8.386%   $195.9727   $195.97   $195.95   $196.00  
  Purchase #6 $123.29   5.807%   $130.4495   $130.45   $130.45   $130.40  
  Purchase #7 $176.79   6.410%   $188.1222   $188.12   $188.10   $188.10  
  7 purchase totals = $796.72       $850.0308   $850.03   $850.00   $849.90