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 $33.32   6.159%   $35.3722   $35.37   $35.35   $35.40  
  Purchase #2 $208.71   5.324%   $219.8217   $219.82   $219.80   $219.80  
  Purchase #3 $81.40   8.231%   $88.1   $88.10   $88.10   $88.10  
  Purchase #4 $200.30   9.392%   $219.1122   $219.11   $219.10   $219.10  
  Purchase #5 $230.86   6.491%   $245.8451   $245.85   $245.85   $245.80  
  Purchase #6 $152.88   4.145%   $159.2169   $159.22   $159.20   $159.20  
  Purchase #7 $49.60   5.377%   $52.267   $52.27   $52.25   $52.30  
  7 purchase totals = $957.07       $1,019.7351   $1,019.74   $1,019.65   $1,019.70