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 $247.47   6.593%   $263.7857   $263.79   $263.80   $263.80  
  Purchase #2 $64.69   5.667%   $68.356   $68.36   $68.35   $68.40  
  Purchase #3 $185.93   9.325%   $203.268   $203.27   $203.25   $203.30  
  Purchase #4 $29.81   7.628%   $32.0839   $32.08   $32.10   $32.10  
  Purchase #5 $209.39   6.338%   $222.6611   $222.66   $222.65   $222.70  
  Purchase #6 $59.28   3.392%   $61.2908   $61.29   $61.30   $61.30  
  Purchase #7 $32.40   4.626%   $33.8988   $33.90   $33.90   $33.90  
  7 purchase totals = $828.97       $885.3443   $885.35   $885.35   $885.50