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 $160.92   8.493%   $174.5869   $174.59   $174.60   $174.60  
  Purchase #2 $214.97   6.317%   $228.5497   $228.55   $228.55   $228.50  
  Purchase #3 $152.27   4.518%   $159.1496   $159.15   $159.15   $159.10  
  Purchase #4 $212.35   12.329%   $238.5306   $238.53   $238.55   $238.50  
  Purchase #5 $221.74   5.721%   $234.4257   $234.43   $234.45   $234.40  
  Purchase #6 $234.72   13.329%   $266.0058   $266.01   $266.00   $266.00  
  Purchase #7 $239.30   11.291%   $266.3194   $266.32   $266.30   $266.30  
  7 purchase totals = $1,436.27       $1,567.5677   $1,567.58   $1,567.60   $1,567.40