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 $46.83   6.653%   $49.9456   $49.95   $49.95   $49.90  
  Purchase #2 $106.53   10.249%   $117.4483   $117.45   $117.45   $117.40  
  Purchase #3 $211.33   9.155%   $230.6773   $230.68   $230.70   $230.70  
  Purchase #4 $35.67   10.624%   $39.4596   $39.46   $39.45   $39.50  
  Purchase #5 $72.49   8.382%   $78.5661   $78.57   $78.55   $78.60  
  Purchase #6 $103.68   11.440%   $115.541   $115.54   $115.55   $115.50  
  Purchase #7 $129.94   11.680%   $145.117   $145.12   $145.10   $145.10  
  7 purchase totals = $706.47       $776.7549   $776.77   $776.75   $776.70