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 $54.72   9.512%   $59.925   $59.93   $59.95   $59.90  
  Purchase #2 $87.62   11.847%   $98.0003   $98.00   $98.00   $98.00  
  Purchase #3 $102.81   11.466%   $114.5982   $114.60   $114.60   $114.60  
  Purchase #4 $16.68   8.671%   $18.1263   $18.13   $18.15   $18.10  
  Purchase #5 $141.57   5.350%   $149.144   $149.14   $149.15   $149.10  
  Purchase #6 $49.28   10.308%   $54.3598   $54.36   $54.35   $54.40  
  Purchase #7 $216.68   10.776%   $240.0294   $240.03   $240.05   $240.00  
  7 purchase totals = $669.36       $734.1830   $734.19   $734.25   $734.10