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 $86.51   11.691%   $96.6239   $96.62   $96.60   $96.60  
  Purchase #2 $65.87   5.186%   $69.286   $69.29   $69.30   $69.30  
  Purchase #3 $60.54   12.861%   $68.326   $68.33   $68.35   $68.30  
  Purchase #4 $172.34   4.112%   $179.4266   $179.43   $179.45   $179.40  
  Purchase #5 $141.30   13.415%   $160.2554   $160.26   $160.25   $160.30  
  Purchase #6 $37.37   8.300%   $40.4717   $40.47   $40.45   $40.50  
  Purchase #7 $7.51   9.402%   $8.2161   $8.22   $8.20   $8.20  
  7 purchase totals = $571.44       $622.6057   $622.62   $622.60   $622.60