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 $213.81   11.796%   $239.031   $239.03   $239.05   $239.00  
  Purchase #2 $197.35   4.337%   $205.9091   $205.91   $205.90   $205.90  
  Purchase #3 $77.51   4.210%   $80.7732   $80.77   $80.75   $80.80  
  Purchase #4 $197.97   6.452%   $210.743   $210.74   $210.75   $210.70  
  Purchase #5 $200.54   9.422%   $219.4349   $219.43   $219.45   $219.40  
  Purchase #6 $18.63   5.837%   $19.7174   $19.72   $19.70   $19.70  
  Purchase #7 $177.96   5.392%   $187.5556   $187.56   $187.55   $187.60  
  7 purchase totals = $1,083.77       $1,163.1642   $1,163.16   $1,163.15   $1,163.10