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 $83.89   12.543%   $94.4123   $94.41   $94.40   $94.40  
  Purchase #2 $197.51   7.122%   $211.5767   $211.58   $211.60   $211.60  
  Purchase #3 $115.86   13.125%   $131.0666   $131.07   $131.05   $131.10  
  Purchase #4 $98.98   8.669%   $107.5606   $107.56   $107.55   $107.60  
  Purchase #5 $65.81   7.297%   $70.6122   $70.61   $70.60   $70.60  
  Purchase #6 $184.89   3.252%   $190.9026   $190.90   $190.90   $190.90  
  Purchase #7 $14.29   4.160%   $14.8845   $14.88   $14.90   $14.90  
  7 purchase totals = $761.23       $821.0155   $821.01   $821.00   $821.10