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 $245.59   8.213%   $265.7603   $265.76   $265.75   $265.80  
  Purchase #2 $21.25   9.505%   $23.2698   $23.27   $23.25   $23.30  
  Purchase #3 $219.40   4.366%   $228.979   $228.98   $229.00   $229.00  
  Purchase #4 $73.55   12.311%   $82.6047   $82.60   $82.60   $82.60  
  Purchase #5 $230.49   4.639%   $241.1824   $241.18   $241.20   $241.20  
  Purchase #6 $59.67   10.667%   $66.035   $66.04   $66.05   $66.00  
  Purchase #7 $205.46   10.720%   $227.4853   $227.49   $227.50   $227.50  
  7 purchase totals = $1,055.41       $1,135.3165   $1,135.32   $1,135.35   $1,135.40