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 $43.29   5.703%   $45.7588   $45.76   $45.75   $45.80  
  Purchase #2 $64.42   10.597%   $71.2466   $71.25   $71.25   $71.20  
  Purchase #3 $39.90   10.255%   $43.9917   $43.99   $44.00   $44.00  
  Purchase #4 $208.71   3.861%   $216.7683   $216.77   $216.75   $216.80  
  Purchase #5 $153.91   10.864%   $170.6308   $170.63   $170.65   $170.60  
  Purchase #6 $237.61   3.252%   $245.3371   $245.34   $245.35   $245.30  
  Purchase #7 $235.66   12.617%   $265.3932   $265.39   $265.40   $265.40  
  7 purchase totals = $983.50       $1,059.1265   $1,059.13   $1,059.15   $1,059.10