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 $177.67   13.477%   $201.6146   $201.61   $201.60   $201.60  
  Purchase #2 $5.41   11.409%   $6.0272   $6.03   $6.05   $6.00  
  Purchase #3 $43.54   6.369%   $46.3131   $46.31   $46.30   $46.30  
  Purchase #4 $170.66   10.381%   $188.3762   $188.38   $188.40   $188.40  
  Purchase #5 $104.71   10.349%   $115.5464   $115.55   $115.55   $115.50  
  Purchase #6 $149.47   13.167%   $169.1507   $169.15   $169.15   $169.20  
  Purchase #7 $176.59   4.360%   $184.2893   $184.29   $184.30   $184.30  
  7 purchase totals = $828.05       $911.3175   $911.32   $911.35   $911.30