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 $163.25   6.791%   $174.3363   $174.34   $174.35   $174.30  
  Purchase #2 $116.83   11.148%   $129.8542   $129.85   $129.85   $129.90  
  Purchase #3 $86.74   5.653%   $91.6434   $91.64   $91.65   $91.60  
  Purchase #4 $233.79   12.708%   $263.5   $263.50   $263.50   $263.50  
  Purchase #5 $122.69   10.487%   $135.5565   $135.56   $135.55   $135.60  
  Purchase #6 $170.71   4.626%   $178.607   $178.61   $178.60   $178.60  
  Purchase #7 $88.74   8.260%   $96.0699   $96.07   $96.05   $96.10  
  7 purchase totals = $982.75       $1,069.5673   $1,069.57   $1,069.55   $1,069.60