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 $235.33   13.673%   $267.5067   $267.51   $267.50   $267.50  
  Purchase #2 $54.58   5.445%   $57.5519   $57.55   $57.55   $57.60  
  Purchase #3 $169.77   3.699%   $176.0498   $176.05   $176.05   $176.00  
  Purchase #4 $177.55   7.361%   $190.6195   $190.62   $190.60   $190.60  
  Purchase #5 $163.73   5.540%   $172.8006   $172.80   $172.80   $172.80  
  Purchase #6 $47.33   3.310%   $48.8966   $48.90   $48.90   $48.90  
  Purchase #7 $59.73   13.259%   $67.6496   $67.65   $67.65   $67.60  
  7 purchase totals = $908.02       $981.0747   $981.08   $981.05   $981.00