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 $34.77   9.410%   $38.0419   $38.04   $38.05   $38.00  
  Purchase #2 $59.38   8.221%   $64.2616   $64.26   $64.25   $64.30  
  Purchase #3 $211.49   12.263%   $237.425   $237.43   $237.45   $237.40  
  Purchase #4 $35.53   5.115%   $37.3474   $37.35   $37.35   $37.30  
  Purchase #5 $183.90   10.185%   $202.6302   $202.63   $202.65   $202.60  
  Purchase #6 $68.93   12.397%   $77.4753   $77.48   $77.50   $77.50  
  Purchase #7 $98.25   3.213%   $101.4068   $101.41   $101.40   $101.40  
  7 purchase totals = $692.25       $758.5882   $758.60   $758.65   $758.50