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 $160.61   5.447%   $169.3584   $169.36   $169.35   $169.40  
  Purchase #2 $226.31   11.664%   $252.7068   $252.71   $252.70   $252.70  
  Purchase #3 $59.80   9.133%   $65.2615   $65.26   $65.25   $65.30  
  Purchase #4 $125.34   8.182%   $135.5953   $135.60   $135.60   $135.60  
  Purchase #5 $250.61   4.620%   $262.1882   $262.19   $262.20   $262.20  
  Purchase #6 $230.88   9.416%   $252.6197   $252.62   $252.60   $252.60  
  Purchase #7 $213.71   7.166%   $229.0245   $229.02   $229.00   $229.00  
  7 purchase totals = $1,267.26       $1,366.7544   $1,366.76   $1,366.70   $1,366.80