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 $156.61   3.627%   $162.2902   $162.29   $162.30   $162.30  
  Purchase #2 $190.86   8.435%   $206.959   $206.96   $206.95   $207.00  
  Purchase #3 $32.98   11.704%   $36.84   $36.84   $36.85   $36.80  
  Purchase #4 $96.35   13.691%   $109.5413   $109.54   $109.55   $109.50  
  Purchase #5 $239.77   7.654%   $258.122   $258.12   $258.10   $258.10  
  Purchase #6 $198.62   8.811%   $216.1204   $216.12   $216.10   $216.10  
  Purchase #7 $77.91   10.290%   $85.9269   $85.93   $85.95   $85.90  
  7 purchase totals = $993.10       $1,075.7998   $1,075.80   $1,075.80   $1,075.70