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 $179.66   6.449%   $191.2463   $191.25   $191.25   $191.20  
  Purchase #2 $123.88   3.401%   $128.0932   $128.09   $128.10   $128.10  
  Purchase #3 $207.64   10.141%   $228.6968   $228.70   $228.70   $228.70  
  Purchase #4 $38.90   11.556%   $43.3953   $43.40   $43.40   $43.40  
  Purchase #5 $113.93   8.106%   $123.1652   $123.17   $123.15   $123.20  
  Purchase #6 $139.31   5.718%   $147.2757   $147.28   $147.30   $147.30  
  Purchase #7 $240.43   11.281%   $267.5529   $267.55   $267.55   $267.60  
  7 purchase totals = $1,043.75       $1,129.4254   $1,129.44   $1,129.45   $1,129.50