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 $245.49   8.743%   $266.9532   $266.95   $266.95   $267.00  
  Purchase #2 $202.97   9.776%   $222.8123   $222.81   $222.80   $222.80  
  Purchase #3 $112.76   7.736%   $121.4831   $121.48   $121.50   $121.50  
  Purchase #4 $54.76   8.389%   $59.3538   $59.35   $59.35   $59.40  
  Purchase #5 $169.78   3.657%   $175.9889   $175.99   $176.00   $176.00  
  Purchase #6 $38.96   4.191%   $40.5928   $40.59   $40.60   $40.60  
  Purchase #7 $179.66   9.793%   $197.2541   $197.25   $197.25   $197.30  
  7 purchase totals = $1,004.38       $1,084.4382   $1,084.42   $1,084.45   $1,084.60